I believe the proper way to define MVP is basically the player who leads the league in WAR. Now WAR itself is an approximation. In reality every person should sort of be creating their own WAR that fits how they view the game in their own head. For hitters this isn't too difficult but the actual WAR stat does a decent job of assigning value. I tend to value fielding a bit less than real WAR does so I don't count it quite as much. So for me I'd fudge the best defensive players WAR down a little bit. I think pitching WAR the actual stat is downright awful so I have to go through a much larger internal adjustment for my personal pitching WAR. I mostly care about things like K% vs BB% and not things like ERA which I feel is a flawed stat and mostly a team stat. Some people really heavily favor context so maybe they give Yelich bonus points for being so good down the stretch etc. The overall premise stands though, you should be able to create a player value in your head and the player with the most value should be MVP. It has nothing to do with how much the team needed you etc, none of that has anything to do with an individual stat. I mean with that reasoning Betts shouldn't be an MVP because the Red Sox could have won the division without him, that just seems flawed.