well most things apreciate mosa ban since she could beat 90% of the meta 1x1 and sweep from there but i think her ban will affect mostly:
toxapex/a-marowak/fini/mantine/mimikyu-the best answers to pheromosa now will have a drop in usage since they aren't going to check a mon present in 99% of teams, of course they will still are viable, toxapex still walls the shit out of greninja, a-marowak still counters koko and nuke everything(specially on TR with rock head), fini and mantine still can defog and counter keldeo(mantine is a mix between toxapex and fini, but i am 99% sure this mon will drop really fast in the VR). but things like toxapex offense will probably dissapear from existence
starmie/beedrill-this mons not only were checked by pheromosa, but they also were really outclassed by mosa, now starmie is the arguably the best spinner in the tier and beedrill is the closest thing to pheromosa OU will ever have again(sad)
gyarados(mega)/porygon-z/rain teams/choice scarfers-it was really sad to have a speed boosted mon being ouspeeded by a freaking fast wallberaker that could kill your mon and become stronger every kill, now both gyarados and porygon can outspeed the entire unboosted meta and this is huge for them.
slowbro(mega)/slowking/mega slowbro-of course ash-gren and koko still a pain in the ass for them, but they can wall a lot of the meta like metagross, lele(king), lando(mega), keldeo, dd zygarde, zard-x and the newcome mega medicham, with the rise of this mons hoopa-u will rise too, not only because he can counter them, but he doesn't need to worry about a bug mon ruling the tier.
mega alakazam/mega aerodactyl-i don't think aero will have a bumb really, but alaka is the fastest mon the in the tier right now and without his greatest check he can abuse of the awesome new tricks he recived with trace(beast boost/protean/soul-heart/psychc terrain) i hope alaka will rise to A- again.