>>21478316The problem when you let something that fast, that strong, and with that ridiculous movepool into the metagame is that it gets a kill literally every time it gets to come in, and the only way to catch it before it switches out again is to run a weird-ass scarfer that they have no reason not to stay in and kill (and your options are limited here too, because it needs to be faster than base ~85-ish to even outspeed Deoxys)
The OU tier devolves into a game of "can my Deoxys get more free switches than yours?" and "guess the Deoxys lure".