Wouldn't you say that locking Tiger behind tech would already solve the issue of Stug-E -> Tiger meta? The Stug-E is vulnerable enough to vehicles that you can easily counter it with a Stuart/T-70 nowadays.
well first off how do you expect to counter a stug-e with a t70 or Stuart when both have less than half pen of the front armor? Players will just take the savings from not teching and put that into a pak or shrecked up pgs.
While I don't think stug-e into tiger would be good, it would still be possible. (since cost wise it would still be about the same as making a teching choice to t4 for a brumbar or panther, both of which only do half of what a tiger does.)
At that point it becomes an okw ostwind type situation. Get a stug-e or two and then support it with a bunch of paks and/or shrecked up pgs till you can afford whatever the next best unit to get is.
If you make it so it has the same cost penalty as all the other call-in tanks it doesn't get the chance to be the next no brain meta. Such a strat would still be possible but the player would have risks just like a teching player would (still reduced ones).
If after that the stug-e is considered bad then you can buff stats later but all tank call-ins should have the same penalty. You can make all the light vehicles callins exempt since they are not a problem and in most cases you would just make them worse than they already are. (although I'm not sure about the puma, but it has little ai so not that worried)