With the current PTS, we ca see some nice buffs to Arcanist, which needed some buffs to actually be a competent DPS.
But we also see some nerfs, pre-release, to the two new mythics. The change to Esoteric was primarily for PVP. It might still see some use there, but it seemed to me like a mythic designed for PVE, and now it won't be used in PVE. I'm not much of a tank, and it's obviously a good change for PVP as the tank meta has been pretty prevalent on that side, but there could have been a more balanced solution for this. Probably just making it PVE only, or slapping the "against monsters" onto the item when it comes to damage mitigation on its first line would have fixed the major PVP issue without making it useless in PVE. But it probably could have been a more nuanced approach that someone else might have more insight into, someone that tanks more than I do at least.
Velothi, with its 5k pen and 15% crit damage and monster damage was a great idea. It would help out low-end groups without touching the high end since it was strictly a damage decrease for anyone that can light attack weave properly, unless you're an AOE dot machine in which case it was maybe comparable damage, but not a damage increase by any means, so it wasn't really a useful slot. It was a DPS increase for a beam Arcanist build, but not by much, and a decrease for basically all other builds. It probably didn't even need a nerf at this point. The only suggestion I might have for balance would be Major Force instead of minor and increasing the pen back up to at least 3k, but it having its own unique buff was what made it at all useful. One of the best dots in the game, Trap, which is a staple on every DPS build, already gives Minor Force, making it less like replacing the buff and more like making it so you get 99% reduction of LA damage, but only get 1500 pen and a 15% damage increase in return, since you'll probably slot Trap anyway. If it's like that, it should be a 50% LA damage reduction rather than 99%, but that defeats the purpose of the mythic. So I'd say just revert it to its previous version. Not that it'll happen, but that's my suggestion anyway since it's the only one that really makes sense if ZoS actually wants to release an item that's useable in some content.