How many of Henri Cartier-Bresson's photos were taken using autofocus?

How many of Ansel Adams' masterpieces were taken with a camera that had an internal light meter?

How many of Walter Iooss, Jr. and Neil Leifer's iconic photos for Sports Illustrated in the 1960s, '70s, and '80s had the benefit of Image Stabilization?

None, None, and None.

The key to being an outstanding photographer is not having the best equipment in your hands. It is knowing the equipment you have well enough to know what it will and will not allow you to do and then working within those parameters to get images that the technical capabilities of the gear at your disposal will allow you to take.

Sometimes that means knowing the different tools at your disposal well enough to be able to choose the option that best fits the image(s) you are trying to make at that time.

Sure, modern things such as autofocus, very sophisticated light meters and algorithms that interpret the information they collect, and image stabilization make it easier and faster to get many images today than it was to get them in days gone by. But that doesn't mean one can't take first class images with anything other than the latest, greatest, most expensive camera on the market.

Should I switch back to an appropriate EF-M lens (15-45mm f/3.5-6.3 IS STM) or upgrade to a full frame body?

Only you can answer that based on what it is, exactly, that you are trying to do. If you need very large aperture primes that aren't available in Canon's current line of EF-M lenses to focus very quickly, then perhaps you do need to move to an EF body.

But be forewarned, the EF 50mm f/1.2 L isn't a particularly fast focuser on even the top tier Canon full frame bodies. The design of that lens means pretty much the entire optical assembly must move when the focus distance is changed. The EF 85mm f/1.2 L is very similar. The mass of the focus elements limit its AF speed as well.

Using adapted Canon EF lenses on an EOS M camera should not, in and of itself, have any effect on performance the way that adapting a lens from one system to a camera from another system often does. The protocol used by EF-M, EF-S, and EF lenses is all the same. The amount of battery power available may have more of an impact than anything else when moving the AF elements of large aperture lenses with a compact EOS M camera.

I am asking for experience with feelings of "fighting your equipment". Am I a bad photographer complaining about their equipment or a photographer hitting the limits of their equipment?

Every photographer who's ever been worthy of the title "Photographer" has, at times, had feelings of 'fighting with their equipment'. That's because there's no such thing as a perfect camera, there's no such thing as a perfect lens, and there never will be! The marketing hype machines of the camera/lens makers and the associated sellers pretending to be reviewers (cough - DPR - cough, cough - amazon - cough) try to make you think, "If only I had camera X and lens Y there wouldn't be any technical limitations that would need to be overcome!"

I am amazed at how, everytime a new model is introduced, the limitations of the previous model somehow seem to grow larger, more troublesome, and even seemingly insurmountable overnight when compared to how limitless that same model was presented to us just a few months earlier when it was introduced as the hot new camera that would free us from whatever limits our current cameras placed on us!

The truth is there are a lot of things many photographers would like to do that no camera/lens has the capability of doing. The thing that separates the great 'Photographers' from the complainers who always blame the limitations of their gear for their work that doesn't meet their lofty expectations based on the marketing hype machine of the camera makers is that the 'Photographers' learn to push the limits of the gear at their disposal while also finding ways to work just within those same limits.

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A case in point: Some folks think the only thing they need to take better action photos and catch the decisive moment is a camera that can shoot at a higher frame rate. Never mind that some of the greatest action photos ever taken happened in times when 2-3 fps was considered blazingly fast if not outright impossible! What is really needed to catch action at the exact instant one wishes is a sense of timing that can correctly anticipate such a moment while having a familiarity with the equipment one is using so that the camera can be triggered just far enough in advance of that moment that the shutter is open when that instant in time occurs.¹

¹ Or maybe one only needs a bit of luck. Just ask Joe Rosenthal. He shot perhaps the most iconic image of the entire 20th century on a Speed Graphic press camera that took several seconds to wind between shots when the decisive moment occurred just as he was turning around from looking in the other direction.

Let's look at it in terms of milliseconds. If you are shooting at 1/1000 second, that means each spot on the sensor is exposed for 1 millisecond during an exposed frame. Even though it takes anywhere from 2-5 milliseconds² for the slit between the shutter curtains to transit the sensor, the entire sensor is not exposed for that entire time with shutter times shorter than the camera's flash sync speed. Many sports photos are taken at shutter times faster/shorter than 1/1000. Even if one has a camera capable of performing tracking AF at a rate of 14 fps (such as the Canon 1D X Mark II), at a shutter time of 1/1000 a total of 14 out of every 1000 milliseconds are being captured by any specific spot on the image sensor and the other 986 milliseconds occur without being captured. There's a 71 millisecond gap between each millisecond that is being captured by the camera. If the 'decisive' moment lasts only 35 milliseconds, one only has a 50/50 chance if catching it by randomly holding down the shutter button and "machine gunning" it for a couple of seconds. If the decisive moment is only 18 milliseconds in duration, the odds go down to one in four.

² the exact transit time depends on the camera model. Each camera with a focal plane shutter has the same transit time regardless of the shutter time selected. With a focal plane shutter, it's the difference between the time the first curtain begins moving to uncover the sensor and the time the second curtain begins moving to cover the sensor that determines exposure time a/k/a 'shutter speed".

If one's sense of timing is less precise than 71 milliseconds, then one would be better off with the 14 fps camera and using the "machine gun" method. But if one has a sense of timing more precise than the 71 millisecond limit of the equipment then one would be better off timing the shot themselves. In practice, many of us develop a sense of when to hit the shutter button exactly one or two frames ahead of the anticipated 'decisive moment' so that we catch the instant we are shooting for with the second or third frame.

I've shot so many American football extra point/field goal attempts that it is pretty much second nature with the camera I use almost exclusively for that shot to use a three shot burst to catch one frame before the kicker's toe connects with the pigskin, put the second frame right on the money as the foot collides with the ball, and catch a third frame with the ball in the air but still close enough to the kicker and the players in front of the kicker that it is still in the frame. If I try it with one of my other "wide bodies" (the slightly slower cameras that I normally use with wider angle lenses) my timing is off just enough that if I want a shot of the toe connecting with the ball it needs to be the first frame in the burst.

The concept really isn't that different for many other things. Full "Auto" exposure mode is for those who have less of an understanding of exposure than the camera's built in algorithms. Manual exposure in the hands of someone who doesn't know how to use it can be a disaster. One is just as likely to get totally black or totally white frames in such a case. But in the hands of one who understands exposure, can read a light meter, can look at the scene and understand how that particular meter (in that particular metering mode) will "see" a specific scene, and knows how to operate the camera to select specific exposure parameters the results are usually better using Manual exposure mode than using "Full Auto."

In the end, gear with higher capabilities can certainly help. But a better camera won't make you a better photographer. It will just allow you to use more of the skill, knowledge, and experience you've picked up along the way. Part of that experience and knowledge contributes to the ability to pick the best tool for the job from among the options one has available.