UT3 vehicles were great and a huge step above the previous vehicles. UT2004 vehicles were fun until you realized unbalanced and relatively worthless most of them were. Scorpion was flat out so bad in competitive ONS maps they would replace it with the Manta. Hellbender was nothing more than a glorified sniper turret unless you could manage to get somebody in the side seat, which never happened. Manta was stupid powerful.
The issue with UT2k4 vehicles was they all died to Shocktape stupid fast. Are you in the air with a Raptor/Cicada? You're getting blasted like a paper plane in a tsunami. Are you driving a Hellbender or Scorpion? You're dead before you get close to anyone. The Raptor was so bad it was actually only ever used as a hard counter to the Goliath in competitive play, it couldn't deal damage fast enough to not die to foot solider unless you crushed them. The Goliath and the Manta were the only vehicles that had a clear advantage over a foot soldier with the Shock Rifle, everything else had a VERY specific role or just died insantly to anyone that was halfway competent.
UT3 vehicles applied armor to every vehicle sans the Manta and Viper, so they took reduced damage from normal weapon fire to compensate for their huge easy to hit hitboxes (I have no idea why UT2004 didn't do this). They also took away splash damage bullets from the Manta because you're using the fastest vehicle in the entire game that kills dudes on foot super easy, you don't need splash damage bullets on top of that. The new Hellbender is freaking amazing and I don't know why the driver didn't get to use the Skymines before. The back turret is way too nerfed, only doing 150 damage max shot instead of 200, but the vehicle is way better overall. Scorpion is a very useful vehicle instead of being complete and total garbage. The Raptor is a legitimate threat with more damaging bullets that have larger splash damage. The Shock Rifle could also no longer knock vehicles around like it could in UT2004 so not being shot around like a ragdoll when you were driving a giant metal vehicle was pretty cool. UT3's Cicada is pretty janky to use and the Scavenger is the worst vehicle in the entire game, the Nightshade is also pretty stupid but only because you can't destroy spider mine traps. Other than that UT3 nailed the vehicle balance and I hope if vehicles come back they use that as a base instead of 2k4 vehicles.
The Orb does need to be looked at. I admire them trying to fix Onslaught's terrible stalemates that go on forever but there's probably a better way to do it. I like the Orb I just think it could be implemented better.