There's an old saying about photography:

Gear doesn't matter.

While true, it is only part of the fuller truth:

Gear doesn't matter... until it does.

What that means is that better gear won't make anyone a better photographer. If the photographer is not applying the proper technique, skill, and knowledge when using lesser gear then better gear will not improve the poor results that are due to lack of skill, knowledge, and proper technique.

Let's look at your examples and compare the results you got using the Nikon B500 with the likely results that might be obtained by applying the same skill, knowledge, and photographic technique using a "better" camera such as the Canon EOS Rebel SL2/200D.

The Gear

The Nikon CoolPix B500 has a 16MP 1/2.3" sensor that measures about 6.2 x 4.6 millimeters. That gives it an area of about 29mm². Each "pixel well" (more accurately called a photosite) is about 1.3 micrometers wide.

The 1.6X APS-C Canon EOS Rebel SL2/200D has a 24.2MP sensor that measures about 22.3 x 14.9 mm for an area of about 330mm². Each "pixel" is about 3.7µm wide.

Thus the Canon 200D has a sensor with a little over 11X the area of the Nikon B500. Each photosite on the 200D is about 8.1X the area of each photosite of the B500. (The conversion factor is somewhat messy due to the two cameras' different aspect ratios - The B500 has a sensor that is 1.3333X wider than it is tall, The 200D sensor is 1.5X wider than it is tall.)

On paper, the larger sensor of the Canon EOS Rebel SL2/200D should produce better results than the Nikon B500. But on paper, your Nikon B500 should be able to produce better results than what you're getting, too.

The "Equivalent" Comparison

When we view images from both cameras at the same display size, we must magnify the image from the B500 by a linear factor of about 3.4X more than the image from the 200D. The increased enlargement magnifies everything in the image - including noise and blur. This is one of the reasons larger sensors enjoy advantages over smaller ones.

Assuming we are shooting from the same camera position that is the same distance from your flat subject, and that both cameras are properly aligned so that the flat subject is parallel to the camera's sensor and perpendicular to the lens' optical axis:

• To get the same angle of view/field of view of the flat subject, we would need to use a lens with a 3.4X longer focal length on the APS-C Canon Rebel SL2/200D than on the Nikon B500.
• To get the same f-number in order to have the same exposure under the same lighting conditions (measured in terms of the field density of light per unit area), we'd need to use the same aperture: f/3.

Since your EXIF info indicates a focal length of 4mm with the B500, that would require about 14mm with the 200D. This equates to a 35mm/FF "equivalent" of 22mm.

The Limitations of Expecting "Equivalency"

Herein lies the first issue with our "equivalency" requirement: There aren't any really good 14mm lenses for the Canon EOS Rebel SL2/200D optimized for flat field work, which is what one needs to do high quality reproduction of two dimensional art. What few options we would have at 14mm and f/3 are also fairly expensive compared to the standard 18-55mm "kit" lens that usually comes bundled with the EOS Rebel SL2/200D.

One of the main advantages of using an interchangeable lens camera is to allow one to use lenses optimized for a specific use case. Placing restrictions that unnecessarily eliminate lenses that would be the more appropriate for a specific task reduces the advantage of being able to change lenses for different tasks.

If we are willing to back up about 2.5X further, the EF-S 35mm f/2.8 Macro IS STM would be a much better lens to use for such a purpose. It's also relatively affordable compared to most other Macro lenses optimized for flat field work at close distances. Even if we insist on using the EF-S 18-55mm f/3.5-5.6 IS STM "kit" lens, it would do better at 35mm than at 18mm due to less geometric distortion in the middle of its focal length range than at 18mm.

The Real Way To Improve Results

For that matter, you would probably get better results with your Nikon B500 if you backed up about 2.5X further and used the camera's zoom lens at 10mm instead of at the shortest focal length of 4mm. You'd also probably get better results if you stopped the lens down instead of using it wide open at f/3.

Most lenses, particularly cheaper zoom lenses, are sharper when closed down about two stops than when they are used at the widest aperture. Of course to use a two stop narrower aperture you'd need to either extend the exposure time by two stops or increase the light falling on the subject by two stops. Raising ISO by two stops wouldn't really increase exposure, it would just increase amplification of the weaker signal coming from the sensor. This would also amplify noise.

As with many problems in photography, the real answer is more concerned with light than cameras and lenses.

Before you decide to start chasing improved photographs via GAS, learn to utilize the tools you already have to their fullest potential.