I think substats need a overhaul In general
Crit, DH being made into one being the chance and the other being damage seems good, I think the current crit/dh scales way too well.
Skill/spell speeds need to be merged, I'd like it if it was also on par with crit/dh scaling for most classes, as you could run a more faster build that's generally more consistent.

Piety/tenacity being more "utility" focused sounds good on paper but the benefits of them are so low, I think theirs possibilities of having special separate meld able stats for defensive, heal rate, utility ect. Could be creative with it like one stat boosting max HP with heal rate, or another boosting defensive cooldowns on tanks.

I also think you should be able to quick switch from melds and maybe even have meld sets but I doubt that.