Both of your examples are shot at apertures significantly narrower than your camera's diffraction limited aperture.

The EOS Rebel T6i/750D has a 22.3 x14.9 mm sensor with 6,000 x 4,000 pixels for a resolution of 24 MP and a pixel pitch of 3.72 µm. This figures out to a DLA of f/6.0

The answer linked above states the following:

With a digital sensor the DLA is the aperture at which the size of the circle of confusion becomes larger than the sensor pixels and begins to visibly affect image sharpness at the pixel level. Diffraction at the DLA is barely visible when viewed at 100% (1 pixel = 1 pixel) on a display. As sensor pixel density increases, each pixel gets smaller and the DLA gets wider.

DLA does not mean that narrower apertures should not be used. It is where image sharpness begins to be compromised for increased DOF. Higher resolution sensors generally continue to deliver more detail well beyond the DLA than lower resolution sensors until the "Diffraction Cutoff Frequency" is reached (a much narrower aperture). The progression from sharp to soft is not an abrupt one.

Further down it says:

So what happens once you select an aperture beyond the DLA? Diffraction begins to negatively affect the sharpness at the absolute point of focus. In exchange the narrower aperture increases the depth of field that is in nominal focus. There are techniques that allow you to maximize depth of field using the widest aperture possible. Learning how to calculate hyper-focal distance (or carrying a chart for each focal length you use) allows you to place the point of focus as close to the camera as possible while allowing for everything beyond that point all the way to infinity to remain acceptably in focus. At close distances and wide apertures the depth of field is about equally in front of and behind the point of focus. As the subject distance increases and/or the aperture narrows, a larger and larger percentage of the DOF is behind the point of focus. Here is a link to a DOF calculator you can use to illustrate this.

Instead of shooting at f/9 or f/11, try opening up to f/6.3 or so, and focus on an object at or near the calculated hyperfocal distance using the DoF calculator. If you intend to display the images at greater than 8x10 inches (or pixel peep at greater enlargement ratios than the equivalent of 8x10" - when looking at a 24 MP image at 100% on a 23" HD monitor with a pixel pitch of 96 ppi, that's like looking at a portion of a 60x40 inch print!), then click the show advanced button and enter your intended display size and viewing distance.

Beyond that, practice good, basic technique for shooting landscapes:

• Use the lowest native ISO possible for your camera (usually ISO 100 for recent models).
• Use a sturdy tripod with a rock solid head to allow longer shutter times required by narrower apertures and low ISO.
• Use graduated neutral density filters to avoid blowing out the sky or underexposing the non-sky areas.
• Use mirror lockup and remote (wired, infrared, WiFi/Bluetooth, etc.) shutter release to reduce camera shake when actuating the shutter.
• As much as possible, shoot when there is no or very little wind. Not only does wind move objects within the scene you are capturing, but it also can move the tripod enough to affect image sharpness.
• Wait for the right light for your location and subject. You can do everything above, but if the light is not right, you won't get the photo you want. Weather, time of year/month/day, etc. all have an effect on the light illuminating your scene.

Bear in mind that most of the amazing landscape photos you see at sites such as 500px and flickr have extensive post processing applied that tends to sharpen the results compared to how the image first looks straight out of the camera. In some cases advanced techniques such as focus stacking and highly detailed lens correction are being applied.