[@Letter Bee]

Hmm, a drain and conversion is already somewhat dicey in terms of overpowered, imo. But if I had to develop a check and balance for someone who specializes in directly manipulating mana (or whatever they call it here), it would take the form of a rate limit, a proximity limit, and a target limit, rather than a weight limit.

One target at a time (at least for now and that's if Scio green lights it all), in close proximity, and at a slow rate. Think damage over time rather than hard damage upfront. 

Instead of seeing immediate results, it'd be gradual, similar to Donovan's effect. Which means in a potential combat situation, Mikhail would be the guy in the corner keeping that DoT applied on the enemy. Something like that.

Edit: Since you already have a mobility limit on Wellspring, and assuming the AoE isn't large, that seems balanced enough to me.

Edit 2: I would have also suggested a cost limit in the form of the drain costing large amounts of energy to use, but doesn't drain at a 1:1 ratio. More like a 1:0.25 ratio or something, but since Scio has a pattern of disliking quantifiers that are too specific (and I personally agree; there are too many messy details there that aren't necessary), I think more organic limits would be better.