To anyone that thinks V's "gameplay" is somehow better than MGS3-4, please, do everyone a favor and throw yourself in front of a train.
V has better moment to moment gameplay, where as older MGS games had better story and scenarios. It's hard to even compare them together, one is a sandbox game with painfully mediocre stealth where as the others are very tight sneaking simulators, with some impressive attention to detail. Fact is that actual combat is much more fun in V, incentivising the loud and violent playstyle over the no-alarms sneaky one.
Survive is actually much better on the stealth front, as the game forces you to learn the ropes early on when you have little resources(and it's a pain in the ass to farm more resources to make bullets, bombs ect even later on), but most people never played that game because they heard a youtuber say it was bad(without any further explanation)
This debate between V lovers and haters is boring. I'm more interested in the "what ifs". MGS4 has fantastic gameplay, but sadly it barely gets utilized since the whole game is a tech demo. This game needed way more levels where the mechanics are actually used, rather than introducing them in a level or two as gimmicks. Where did the whole faction system go, one where you would have several countries fighting on the battlefield and if you pissed them off there would be consequences in later levels?
I think V was also going to focus a lot more on stealth early on. The best sneaking segment isn't in the game, it's the entirety of Ground Zeroes. If you mod the game to port the entire map over so you can do freeplay in it(something that was planned at some point by Konami BTW), you can tell just how tight the sneaking elements of the game are, but that's rarely utilized in the actual game where most of the map is a sandbox. It is hard to navigate vehicles in that tiny map as well, forcing you to engage on foot like in the other games. It's way too easy to just summon a tank or a helicopter strafe run in the final game, or just snipe everybody with a silenced rifle. GZ and not-Guantanamo Bay feel much closer to the older titles than what we got in the final game.
4 and GZ show what could have possibly been a perfect MGS game, but both times the opportunity was squandered. That's why the trilogy is still supreme in pretty much every aspect, even when combat is much better in V for example.
Metal Gear is a very diverse franchise and you will just have to accept that some games are too radically different from others to compare them. Where do the isometric titles fall, for example? Do they "suck" simply because they lack the gameplay elements of later games or the story isn't as intriguing, convoluted or deep as the 3D entries? There is several radically different kinds of games in the franchise: The isometric ones, the "main" trilogy being what most people think of when they hear the name, the sandbox management autism Big Boss games, there is MGR and Survive that don't really have any equivalents and then there is whatever the hell Acid games are. I guess MGO used to be a thing, but the earlier iterations died and the current one on 5 is dead. It is incredibly narrow minded to throw most of the games under the bus simply because they are different than the ones you personally like.