... I don't know what would be the best course of action here since the UC has a narrow window and IS are difficult to touch.
This is a problem create by allowing increasing powerful unit available earlier. The window of opportunity for some of those units has become very small and thus their shock value has been increased too much to even be considered to be built. That can easily lead to snowball effects.
Imo the pace of the game should be slowed down allowing more time for each phase of the game and more more options should be available for to counter light vehicles.
For instance Ostheer could get the 221 in durable version with limited AI but good at fighting cars and snipers and then 222 could be be delay become more expensive and become more AT oriented.
Flame vehicles could have their DOT moved to an ability so that they remain effective but for a limited timed.
All that would reduce the need for early AEC or for an OP T-70.