What to do...

i doubt it will Et better using a brake.
I have had more motor than this and car 60 footed and ET’ed identically off foot or brake. If the convertor is right., that will most always be the case.
9 sec, 3350 pound car going 1.34/1.35 either way on leafs

I can’t disagree really. But I’ll say this most of the time lost foot breaking, from what I’ve seen is in the driver not the car, and the trans brake helps the driver drive better. Less things going on. Leaving on a button at stall is easier for less experienced drivers. We all know you’ve been at this a while.