"I bet the topdressing guys who operate at low level, day in day out, don't even do max rate turns at such a low level"
Maybe not at exactly 100' but the whole industry is pretty much based on saving seconds, including in turns, in heavy aircraft at low level. Many turns are at the max rate - at which they can get away it. The difference is that such manoeuvres are trained for and it become a specialist technique. This is a reason why there is a need for an agricultural pilot rating.
I have reservations that the average flight instructor would really be up to the task of instructing max rate turns at 100'. I'm not trying to bash instructors. It's just a specialist thing and with limited returns compared to the risk.