There's no point in negating Focus Sash; the turn you used to use Magic Room pretty much makes your next move a 2HKO, assuming you can KO the Focus Sasher in one hit. Same goes for type-resist berries, the Pokemon can set up while you use Magic Room. Leftovers recovery for 5 turns usually isn't critical to a Pokemon's success, it's not worth sacrificing a turn, especially if your leftovers are negated too. Life Orbers and Choicers can deal, and they may even have freedom of move choice for those 4 turns which could even up doing more good than harm.
Sub-Berry users are just rare, and they probably wouldn't keep subbing if Magic Room was in effect.