The tank thing makes sense, I even think earlier BF's had the same thing. The 'weak' spots (which I didn't think even existed until a few days ago after fighting vehicle vs vehicle for about 30 hours now) are the tracks and underbody. The top is armored. The idea with c5 is you plant it under the tank and detonate it, albeit very hard to accomplish. The biggest indicator of 'weak spots' is any tracked vehicle. You can basically fuck up their tracks and immobilize them until repair is off CD and then have your way with them.
The game isn't Battlefield anymore, it's Warthunder or World of Tanks. You just play infantry when you acn't play a vehicle, but vehicle gameplay is THE game. Been running a fully kitted Bolte and that shit is bonkers. Fast, tanky, and can shoot helicopters out of the air AS THE DRIVER without aiming. Feels right. The 30mm grenade launcher is an unbelievably strong anti-infantry weapon. On the Aerial side, they actually might be balanced. The Gunships with repairers on board can be tanky as fuck, but you can hit the passengers out. If allowed to exist they can decimate vehicles and infantry and almost solo cap points. Attack choppers are pretty great anti-air and decent anti-vehicle, but except for the forward gunner can't do much against infantry. Little Birds are great at harassing slower aerials, but are not nearly as good at killing infantry as you'd imagine. The 20mm cannons suck big dingus, the minigun is ... a minigun, but it's hard to sit in spot and destroy them without getting zapped. I've not fucked with the Jets, but they seem to be S-tier anti-air, and C tier anti infantry/vehicle. Weirdly well balanced over all.
Some of the cool vehicle shit is gated behind stuff like 150-250 kills/assists so unless you're lucky enough to get a driver/gunner who is competent it may take a long slog to actually get up to speed where they're very competitive. Stuff like the boat/bolte are definitely worth leveling. The LAT has a nice 50mm weapon for anti-vehicle but does shit all against infantry and offers 0 protection to drivers and gunner. The boats however have ballistic glass and recover fast as fuck. The Bolte is just OP all around, but it has weak tracks as I mentioned before so you can get it stuck and pound on it fairly well.
The guns are all shit though. PP-29, any DMR, or shotguns. Those are your options. Snipers are okay, but basically just for counter-sniping. LMG's have 0 point with their bloom and recoil. AR's are useless except mid range and even then the PP-29 will beat it out most of the time.
TL;DR This ain't CoD, this is Twisted Metal. Play it like it.