I disagree that bigger cameras are better for macrophotography. I say this because of the physics of how light works in macrophotography, which matches my experience doing macrophotography with larger cameras (6x7cm and 4x5").
The long story short is that reducing the aperture has two effects on image sharpness. Smaller apertures increase the depth of field, bringing more of your scene into focus. Smaller apertures also introduce diffusion, which makes the whole image softer. This tradeoff means that there is a medium aperture which makes your image as sharp as possible.
Photographing people with a 35mm camera, the aperture which maximizes sharpness is often achieved with apertures somewhere around ƒ/5.6 or ƒ/8. It is advantageous to use a 35mm camera because the larger sensor size can reveal more detail and capture more light. 35mm also gives you access to larger apertures and those nice, blurry backgrounds.
In macrophotography, large cameras just aren’t as advantageous. The small apertures that you typically use will produce soft images, and the soft images can be captured well enough on a small sensor. Small cameras give you very blurry backgrounds to begin with, so you wouldn’t choose a large camera to blur the background. Additionally, small cameras require less lens movement, proportional to their size, to focus at the short distances required for macrophotography.
I do some macrophotography with my RZ67. Mostly pictures of flowers. It’s fun, but I know that it would be much more convenient to use a smaller camera, and I wouldn’t be sacrificing image quality. One of the big reasons I use the RZ67 is because it uses a bellows to focus, and the bellows is long enough that you can focus very close. However, there’s a lower limit to the size of the subjects I can comfortably photograph, and if I were serious about macrophotography, I would use a smaller camera.
Summary: Large cameras are better at taking pictures of large things, small cameras are better at taking pictures of small things.