It is beneficial to no one. This is a mechanic that should never be in an FPS Halo game.
Not only does it disrupt team skill and makes vehicles even more overpowered. I see your concern with "bad drivers" and stuff but if you join a public game by yourself you should expect that. If you join a public game with your friend then you guys should decide what role the other player gets.
Imagine a Mantis that just camps behind the base all day because they can get repaired and never destroyed. I understand you like this, but it is one of those "sounds good on paper" ideas. Don't forget to mention 343i should actually fix Halo multiplayer first before even adding new drastic mechanics. Game development is no easy task my friend.
Now this isn't a bad idea it just has no place in public Halo matchmaking. I can see it being used in custom games now that could be fun, but like I said. Let 343i balance and fix all the wrong they have done first then think about adding new mechanics