I said at the beginning of my reply that Prestige still exists, but it's less prevalent than it was before, and that's just the nature of the game being as old as it is. I mean- sure some people are completing their first Normal, Heroic or getting their first Cutting Edge, so this is a big deal for them and probably many others in the future.
Quality of Items hasn't meant anything for a long time, all Legion did was through Orange is the new Purple in the mix, and here we are. Orange items previously were the culmination of an entire teams work to help one person achieve a thing. Sometimes it was dps, sometimes it was healers. The thing they moved away from was taking that 'special moment' of orange-y goodness from a single person, and giving it to everyone. I feel like this has a mixed result depending on who you talk to, but this all comes down to personal perspective anyway- so there's no use really arguing it. Some love it, some hate it.
As of this post, I currently have just under 400 mounts on my main. I have a small selection of which I'm proud of, have memories attached to, or that I favor because it took 653 Al'akir kills to get. I don't know what mounts you're referring to as 'free', but in my opinion I couldn't give a single pickled fuck about what anyone else is rolling around on.
And I'm sorry, but just because people can clear a raid on Normal, that doesn't in anyway put them on the same playing field or even in the same stadium as the people that clear Mythic- they don't even see the same version of the final boss or many fights that Mythic raiders do, and I'm absolutely okay with that. Rolling around with Realm First titles and Achievements is an awesome feeling, and doesn't diminish the 'accomplishment' at all. If anything is diminishing the prestige of raiding, it's not the lower difficulties, it's Mythic raiders selling clears- which again, is something I'm fine with.