@glyphiks is correct. Amass lowered their ratings I think. IMHO, this is probably for CYA reasons.
An XT90 can probably do 90A continuous, that’s 24 hours a day. And probably 180A for a few seconds. You likely couldn’t even stand on a board that was drawing any more current than that anyway.
MR60 are generally going to be just big enough to handle any load a normal 63100 or smaller esk8 motor will be drawing. I haven’t had any overheat, nor have I heard any reports of it happening. I’ve got one motor set at 165A motor max using an MR60 with no issues.
Also see this:
So you can see that a 12AWG wire will burn before the Amass brand XT90 gives up. In one experiment, the XT90 was desoldering itself above 270A. It was carrying 270A for ten seconds.