Camera advice? (Bundle GAs inside)

As Yirg said, it's a huge consideration. Mirrorless is arguably the future over DSLRs and Nikon/Canon both suck at mirrorless right now.

Dominating the market means little, just ask AOL.

So "plenty of reason" means easier to find accessories? What accessories exactly are you referring to? Do clue me in.

This budget isn't sufficient for a camera body of the two mentioned in the poll and suitable lenses, which at the very least need to be a wide-to-short-telephoto kit lens (e.g. 18-55, suitable for everyday photography, trips, street photography, landscape), and a long telephoto kit lens (e.g. 75-300, suitable for shooting nature and animals).

His main options are to increase the budget or get a lower tier body with those two lenses (or a single one cover both ranges, but that won't save any money. It will only result in compromises in optical quality). Of course he can decide to get one of these two bodies + only the short lens, but this would be pretty useless for shooting nature and animals.

In my opinion a lower tier body + 2 lenses + an external flash unit capable of bounce flash is likely to be a more useful kit in more situations than a higher end body and a single kit lens. Even more so if your friend can't point to specific features which are important to him. Just getting something expensive for the sake of getting something expensive doesn't make much consumer sense.

By display I mean printing vs. web display. Displaying the pictures on the web is far less demanding than printing large, which means there's less need to split hairs about minute differences in image quality (aka "pixel peeping"). Even FullHD resolution (which is higher than what most people post on social media) is only 1920x1080 px, which is close to 2 MP. That doesn't sound very high, now does it?

Well, then I would look up the compatibility of said lenses and go with that brand. Having a range of lenses is better than the newest processor or sensor; a great lens can take a fantastic picture on a garbage camera, but a garbage lens will always look bad. Good glass retains value.

I'm pretty sure the 7200 can use most Nikon lenses, as well as the 80D for Canon. If his uncle mostly has older non-autofocus lenses then it's up to your user, as he will still have to use the lenses manually.

What lens mount, and will his uncle be willing to let him borrow lenses?