I suspect all light vehicles suffer from the armour values chosen. These roughly seem to follow historical lines ( UC had 10mm at the front and 5mm back corresponding to 10 and 5 in the game files) though unfortunately the bullets and heavier armours do not!
This is particularly noticeable with the medium and heavy tanks, A PIV certainly didn't have 200 and odd mm of amour nor a Cromwell 100 and odd. These have been extrapolated out for gameplay reasons I'm guessing.
Nothing but armour piercing rounds at 90 degrees and very short range ( and then mainly tungsten cored ones which were taken out of service in 1941) would penetrate 10mm of RHA but in game the average jack bullet will do so once in ten shots if I understand the mechanics.
So whilst some vehicles ( heavier) appear to have been balanced some ( lighter ones generally) retain insufficient armour for their intended purpose.
The whole point of troop or support weapon transports was to render them nigh on invulnerable to sporadic or non focussed ( even tanks went down eventually to highly accurate and focussed HMG fire, especially molybdenum starved German armours) small arms fire and artillery splinters, yet most of the light vehicles in game go down remarkably quickly to anything with a high rate of fire. Whether Commando stens or an MG42 it is just a matter of time. 9mm subsonic having a penetration equal to a 7.92 is borderline amusing...
Overall this leads to a tech up at all costs approach to the heavier armours whereby light vehicles are useless later in the game, which unfortunately nullifies the combined arms approach somewhat.
Now if teching also increased the armour ratings of the light vehicles they would still retain a buildable use in the late game. I don't mean a UC flying around with 100+ armour ratings, merely making them and all other scout or utility vehicles less prone to small arms once you hit Tier3 for instance. Unfortunately this isn't how the game is designed.
this a true but there is an issue that if light vehicles cannot be countered by small arms then the only other options are HMGs (hard to position, relatively low damage, easy to stay out of the cone) and AT weapons then early light vehicles will have no counter. adding (lol, pipe dream) light AT guns like the m-42 would of course solve this but that's not going to happen.
the same issue is present with light tanks and standard AT weapons.