As someone who started with Tekken and then migrated to Capcom games, Tekken is quite different from Marvel but some of the fundamentals I picked from Tekken actually transferred well into Marvel.
Yeah there is a shit ton of characters in Tekken but a lot of characters play similarly and there are a lot of overlapping normals and vanilla moves. Also as far as basic tools and movement go, the characters are very similar (all characters can run, have same wake up options, parry option etc). The playstyles in a game like Marvel are extremely different and so are the base tools per character. You have a character like Morrigan who can fly cancel her air specials... but can't ground dash while you have a character like Vergil who has no air dash but very fast ground dash. There are hardly character playstyle archetypes in Tekken, like you can't say one character is a "zoner" while the other is "rushdown"... there is no real distinction like that. Yeah there are characters who are more grapple or style heavy than others but it's not nearly as prominent as the 2D games.
In Tekken there are rarely terrible/lop sided match ups, there are just characters who are slightly better than others (ie 5-5, 6-4 match ups). If you are good with your character and have good fundamentals/reactions you are not limited in a match and can always make something happen (there is no block damage either so it's all a matter of making the reads and spacing yourself). You also don't have to deal with the standard bull shit of a Capcom game mainly ambiguous cross ups (no real right/lefts in Tekken, it's all high/low mix ups with throws). I still have a hard time blocking right/lefts in Marvel. Also in Tekken you default to blocking high and reacting to lows, in Capcom it's the exact opposite. Not a big deal though.
The similarities between Marvel and Tekken are that when you get hit by a move capable of continuing a combo (a launcher, bounce or some sorts of sweeps) it's going to hurt and the combo is going to be long. Further more after the combo has ended it is usually going to put you in a bad situation where you have to guess on your wake up. This can end rounds quick... hence the standard of 3/5 rounds in Tekken. I haven't played TTT2 much but that's how it was in Tekken 5 at least. The next similarity is the movement. Now granted Tekken does not have any sort of aerial movement but you need to be up to snuff with your ground movement. Side stepping, wave dashing, back dashing... you are constantly weaving in and out. Similar thing in Marvel just replace side stepping with air dashing. You always want to be in a good position and avoid bad situation in both games because if you are in a bad situation you have to guess a mix up and if you guess wrong it's going to hurt. The roster sizes in both games are also really huge now so you are always bound to find at least a couple of characters you want to play/try out.
Even with the tag mechanic in Tekken, there isn't much synergy among pairs where you have to match up character tools with character requirements. You essentially are able to pick 2 characters that you like or are good with. I played Jin and Heihachi in TTT with the occasional Jun thrown in. It just happened that those characters had some synergy gimmicks attached to them but I didn't use it a lot. Marvel on the other hand you have to think really hard and really invest in the whole aspect of team synergy. You don't just pick 3 characters you are good with, pick whatever assists and put them in the order of your liking, chances are that team is going to be ass. The reason why the Marvel OT is still going very strong is because people are constantly theory crafting new teams with new combinations. That is the appeal to Marvel, the whole 3 on 3 team play is what draws many to Marvel and it's the same thing that draws people to games like LoL and DOTA. Because the combinations are so vast you can't prepare for particular match ups and much of your experience/training comes from within the match itself. That's why I laugh at the idea of 2/3 Marvel, I mean that's not nearly enough time to scope out the tech on the opposition's team. Hell the first to five exhibition in the RayRay vs Moonz match, even that was not enough to show all the tech that Moonz had on the team.
Truth be told, if MVC3 was just a 1 on 1 game or a simple 3 on 3 tag game (no assists, DHCs, TACs, THCs, CCs, X factor etc) it would be ass. Too many bad match ups in the game but the team aspect severely cuts down on the match up problems (Haggar vs Magneto is on paper very bad for Haggar but Haggar with just a projectile assist can beat Magneto convincingly and consistently). I am surprised there aren't many other games like this, I mean Skullgirls sort of tried it but it just didn't had the vast number of characters needed to make a game like this work. If everyone is using like 5-6 combination of teams in a game like that... it's not much better than playing a normal fighting game with 5 top characters and the rest being ass.