I have a photo of a train that was taken by me 25 years ago with a 2.1 megapixel Sony camera. The jpeg file size is about 370K. It prints good up to slightly over 8 X 10", but enlarging further produces diminishing results, and cropping is not worth trying as any loss of the 2.1 mega pixels available prevents the 8 X 10" size quality print. The photo attached is straight from the camera with no POST alterations or adjustments
Do you need more megapixels? Well it sure helps if the photo taken will need to be cropped or enlarged to larger than 8 X 10" size, but otherwise for me it's a waste of camera money. The old 35 mm film camera photos with film taken on 100 ISO Kodachrome film compare today to about a 16 megapixel shots, so any photo with higher megapixels just makes it easier to crop without image quality loss over what can be done with a good old 35 mm camera and quality film. With the excess megapixel capability it does make it a whole lot easier to produce quality photos of any size needed by the customer, but it isn't much of a benefit that I need for most day to day photography. So for me I just see no reason to spend even more money on bigger cameras and higher megapixel capability. The other problem created with larger megapixel capability is the file sizes created. You can fill a solid state or hard drive very quickly with photos that are "too Big" than your actual need, and post processing these oversize photos forces bigger and bigger computers and slower edit times too. Why spend the money, if you don't need this size camera and computer for the kind of work that you do? This is pretty much no longer a race for better capability.
Now, I'll tell you the truth about what I am presently using. I have a Canon 90D camera, two 77D cameras and a Fuji that's about 16 megapixels. They do everything that I could want. I haven't gone mirrorless, yet, since all of my needs, both in studio and out, are handled very well by these cameras that I already have. In the field, with one of my 77D cameras and my 18-400 Tamron lens I can take shots both near and far without the need to change the lens. Today, it's the lens quality, more than the camera that creates the high quality sharp focused shots. I haven't gone mirrorless because my cameras are relatively still new, and I'm kind-of waiting for the 2nd or 3rd generation of mirrorless cameras, figuring that the first generation are likely full of quirks that haven't been fixed yet by the camera manufacturers. My age is beginning to restrict my love of photography (83 now), so I may not ever own a mirrorless camera before the end arrives. It almost did last week and I needed yet another heart surgery. I am doing great again after this. So I am quite happy with what I have and I'm wondering why I should ditch it all and start over with new cameras and lenses at my age. I don't think so, at least not yet.
Charley