In the brushed motor days, I would often add some forward roll with my throttle trims if the motor had more drag than I liked. I thought I read this was a no no with brushless system. I also see that Tekin has a "push control" feature that seems to do the same thing. Is it bad to use forward roll via trims on today's brushless systems?

Some guys do it still.
The main issue is: some radios move the full throttle point with the trim so 100% is now 95%. then even if you move the endpoint have no way of setting the EXACT full throttle point that the esc expects. Also if this happens you may now have over 100% brakes which may confuse the esc, reseting it.

Personally just I learn to hold some throttle and not just release it and allow it to return to center. Then again I run Tekin so I can set it exact in the ESC

Either way you are tuning for your slowest corner. Is your slowest corner neutral or do you still need some throttle to be fast, if so then maybe it will work for you.