Obv a lot of the megas are now very usable (i.e. Mence, Diancie, Metagross, etc.), so a lot of teams that were previously suppressed by Mega Ray now have a lot more flexibility in their builds (Double Dragon Ray+Mence core and Diancie+Gira-O support core ftw). PDon really doesn't absolutely have to run DClaw anymore since its only main target I can think of rn is Gira-O, and since Ho-Oh balance seems like it'll make a resurgence due to Soul Dew Latis being allowed again, Stone Edge might be the preferred move again over DClaw.
POgre got a lot better as well, since now it isnt shat on repeatedly by Mega Ray and the variety of teams it does well against (balance, bulky offense) are coming back into the meta, it can just bork them. Dialga gets lol'ed on by CM sets now, in addition to Blissey getting wrekt after a boost or 2, so the real good checks to Ogre as a whole have diminished (mainly to Palkia, which is ehh, in addition to the Soul Dew Latis). Also PDon does not like taking a +1 Ice Beam, like at all.
I feel YGod and Darkrai got a whole lot better in the semi-gen shift, as the Latis just became prime targets to KO, in addition to Lugia being a solid check to PDon and therefore get a rise in viability. Yveltal in particular has gotten some cool buffs since Tailwind is amazing and with Lati support being very helpful, it can do a lot more to support its team than before. Physically Defensive sets are also pretty good now since it can actually stomach a hit from MegaMence and with Mega Ray gone, it can actually do its job effectively.
tl;dr
Megas are gud
Primal Kyogre is gud
Ygod is gud