Light vehicles in WT are really usually not firepower-deficient. As for armour, that’s sort of the point, it’s way more situational than mobility. You can play around lack of armour by not being hit and being careful, but you can’t similarly mitigate lack of mobility with gameplay. And since WT is a game about capturing points, where the meta is getting to power positions early, mobility is always more important.
To this you should add the fact that usually, TDs are turretless and have awful targeting speed. Sometimes very long reloads as well. They don’t usually capture points first, they don’t get you easily into CAS…
Currently the game doesn’t really make that distinction. A light is a light. If you want IFVs and APCs to gain a “support mechanic” in exchange for losing a mechanic that “proper” light tanks have, I’m all for it.
When it comes to TDs and SPAAs however,
You’re thinking about it from a “neat and orderly” external perspective, and from that POV it doesn’t make much sense, since the focus of TDs should be killing stuff.
However, WT is a game, and not even just any game like say Flames Of War, but an MMO shooter. So I look at it through the lens of, what do these vehicle classes need?
SPAAs need to be able to resupply without having to stare down tanks to get to a capture point. Their job is to engage planes, that’s what they should focus on and they need help doing that.
TDs will need to frequently relocate anyway because they’re usually more visible than a concealed SPAA from the air, but once again not having to rush to a capture point with a vehicle that is slow and turretless will make them a bit more flexible, which is welcome. And the ability to go hull down anywhere, while unfortunately not very useful on a lot of CQC maps, can definitely make your TD life easier on occasion. This is especially true for ATGM carriers.