I am a bit late to party, but here are my few cents. There is really no need to remove tier-scaling, just make it inherent class ability and apply to
anything in mindslot. Make gems more worthy: change damage type of auras to dazing lighting (tier-scaling chance of daze), cleansing flames (tier- and mindpower-scaling number of effects) and slowing-physical, all applied by mindpower. Maybe even other effects, depending on type of gem wielded:
- reduce cost and cooldown auras
- give permanent tier-scaling psi-regen (for mindlash)
- give auras additional effects when sustained (+global speed, +all resist, +plain armor)
- make it possible to sustain all shields/auras at once
etc. Artifact gems should get especially powerful, game-changing buffs. Right now wielding gems is pointless: their buffs were designed for 2 of them to be worn by golems (supposedly, to prevent them from becoming OP), not for class trading them for two-handler/mindstar set.
EDIT: actually, just make gems on-par with weapons by giving them one base quality for each type (to make up for lack of melee attack) and some number of random egos, invisible for anyone but mindslayers. Artifact games would have qualities of randart and Lifebinding Emerald would essentially be analog of merchant randart with randomly-generated huge number of egos.