specs of su-76 is fine, except the timing, expecting a 260/75 8 pop TD to compete in late game should be limited, just like any other contemporary ''light'' tanks.
Though i agree that it lacks a place, it isn't bad whatsoever.
it performs well for its cost, so perhaps change the su-76?
-nerf some aspects for a cheaper price, to make it more viable and arrive earlier.
-buff the su-76 for a true multi-purpose like it was IRL for a cost increase.
or delay T4 for all faction so that window of opportunity for all lower is increased...