Yes, mind flay is way too weak. I think having Impending Doom, Molten Core, Beacon of Shadow and maybe Nightfall (let's say Nightfall reduces channel duration for Mind Flay) interact with it would help a lot. I'm okay with removing the slow component of the spell if certain MEs are used that buff it. I'd say anything that interacts with Shadow Bolt should probably also interact with Mind Flay as they are both filler shadow spells.
Another thing I realized - Devour Mind does not apply shadow embrace and only applies 1 stack of shadow weaving (on initial tick). IDK what the purpose of Devour Mind really is. It buffs Mind Flay but it is sort of like a replacement for Mind Flay. It also really requires 3 talent points into improved Devour Plague.
Instant cast Vampiric Touch and Unstable Affliction (epic RE maybe) would also be a great help. I don't PVE; in PVP it seems like DOT specs are almost useless now. It's common to get all my DOTS up on someone (COA, CORR, SWP, VT, UA, DP) and they just walk up and blow me away in 3-4 GCDS and never even get low on health.