The legacy of Final Fantasy? What difference does that really make in the grand scheme of things? Sure, one can look and say x,y,z is how things should be done based on past examples. I’m more concerned with what is going on today, and not so much with what took place in the past. You speak of newer people probably not being able to see the flaws in FFXV, but wasn’t that the EXACT same thing that happened with FFVII? I believe so. Hell, there are people still today that will talk up FFVII like it’s the Holy Grail of gaming, despite the reality that the game has some glaring flaws. That isn’t taking place with FFXV on the vocal side. People acknowledge the game has flaws, but despite that most are still able to enjoy the game greatly. Perhaps that boiled down to the pros of the game being so significant that the cons ended up not being as major of a problem for a good number of people. A game with flaws =/= a game that will be chalked up as a bad game. A game from a design outlook could objectively have the best everything, but none of that matters if it fails to connect with people.
Also, FFXIII objectively from a vocal aspect is the most criticized mainline game in the series. The only game imo that would have gotten more criticized would be FFII. Luckily, the internet had not blown up during the release time frame of FFII, therefore it evaded that bullet. If you want to argue that FFXV has gotten more criticism, then not only will you be barking up a tree, but you will also give me proof of how out of touch you are with the vocal part of the community.
One more thing: Critics can have a bias rather that is in support or against a title. I personally tend to take some things with a grain of salt.