I used a newfangled calculator, as you didn't directly instruct me to do, and I can apparently run, splice, and dead short an embarrassingly irresponsible amount of current through a $1 plastic box. I just looked up some boxes, outside of your link, and I concede that the rating is no longer applied? WTF. I'm getting old, cranky, and I'm wondering who bribed who... Because back in my day one would get their lunch break disappeared if a run capacity was more than what was LITERALLY on the label for the box (every one had better have been 20 amps per gang or your ass was driving back to the store). What written word is keeping some nutbag from pulling 100 amps through a single gang box? That terrifies me. The only rating I found, in amps, was for a junction box in the UK (pedantically not in Europe), but that isn't for the enclosure it is for the screw terminals that are basically molded in.

At this point it's safe to say that I'm scared for the children, and I'm a cranky old man.