I feel like vehicles used to be easier to take down though. With a shield it is much more difficult, especially if you are solo queuing and no one on your team is shooting at them but you. I remember in H2 the vehicles were way easy to take out in BTB. I never got in them for that reason, unless it was a hog to move a flag.
Personally, I think it's fine if the vehicles are difficult to take out. I don't think they should be so weak that you can take them down without the help of your team, unless you have some kind of anti-vehicle weapon or EMPing grenade. That's just personal preference, though.
I never played BTB in Halo 2, and I mostly stuck to playing Heavies in Halo Reach and 4, so my perspective on this could be a little biased but I never got the impression that vehicles were particularly overpowering in Halo 5's BTB. In fact many of Halo 5's BTB maps currently don't have any vehicles besides a Ghost and a Warthog anyway, and it seems much easier to get battle rifled out of Warthog turrets too.
Stating is when an opposing team does not go for the objective and just slays you.
ok, I always referred to that as "stat padding" but I get the idea. In any case, I'm not sure if I fully buy the argument that maps should have weaker vehicles because one team could potentially gain control of all the vehicles on the map and stat the other team. I don't think it's possible to design a 100% stating-proof map, but if you tried to, you'd probably end up with a boring map that barely has anything besides the weakest weapons and vehicles.
I mean certainly stating would be made easier on a map with, like, 20 Hannibal Mantises but there is always going to be stating no matter how many strong vehicles are on the map. So map designers should find a balance between not so many vehicles that stating is easy, and not so little that the map becomes bland (by the way, I feel like Halo 5's BTB is mostly leaning too far towards the latter right now). Matchmaking itself can also help prevent stating in a different way by using MMR and stuff to match full teams with other full teams instead of with solo players. Basically, I don't think it's completely necessary to water down vehicle play just because stating happens sometimes.
I understand that you were just making a suggestion and vehicle-free BTB might be a new thing that could appeal to players who like to play regular Slayer but would enjoy a bigger team size. I get that, maybe vehicle-free BTB could be an extra game mode alongside Heavies and/or objective, and I respect your suggestion but I feel like that would have been more interesting in a Halo game where BTB actually feels significantly different than regular Slayer. In Halo 5, BTB currently feels far too similar to regular Slayer when it has so many maps like Eagle Square and Port Authority. Just my opinion.