Luchs, Scott, T70, Stuart, etc. They have some good killing potential, but need to stand up slightly better to AT imo. Gettin two shotted by Zis and Paks is a bit too harsh, they should survive just a little bit longer so that they have maybe 10-20% hp left after a second hit. If you drive in to an AT guns arc at all it is usually dead unless you were driving across it at full speed, because even with instant reaction to seeing it, it can get off two shots before you can change direction or drive through it a lot of the times. Basically it should take a little bit more active effort to kill them, right now the burden falls more on the person trying to keep it alive because they die as quickly as infantry died to FHT during the beta glory days.
For when they hit the field the super early game vehicles (Kubel, M3, etc) have a similar life expectancy if not better. Of course you can keep them alive a very long time if you only passively use them to target the solo squads that are trying to back cap you, but using them in flanking timing pushes is almost too high risk, because one surprise ATG in a place you weren't expecting it will get off the second shot more often than not even when you immediately react to it.
Not saying that overall they are underpowered because some of them (Quad, T70, Luchs) are way too efficient at just driving on a capping squad and killing it 90% of the time in retreat, but thats another topic and I'll address that later.
I don't think giving them more health would do anything but make light tanks -> heavy tanks, 3 shots is quite a bit when you think of the meta mid game.
-Imagine having 2 Paks/ 2 Zis's waiting for an enemy tank to roll in, with 1 volley you have the element of suprise, 2 volleys not really. Light vehicles would never die if you micro'd them correctly.
-You'd literally have to: volley (2 At's), snare with infantry, reposition At, volley once again. That's overkill due to the fact noone builds 2 At guns normally early-mid game.
-Lights would last foreverrrr, plus you couldn't just keep chasing for the kill, a vet player would have small arms just waiting for your At support.