I dont generally have a problem with direct combat spells but mana bolt is just too good.
Not only is it the spell of choice to drop street sams but also nukes everything 'living' with aplomb too. Mundanes, spirits, wizzers both physical and in the astral and spirits count as destroyed not disrupted! I mean come on, this is why it is a must spell. And am no better I take it every time.
What I would propose is a house rule: Spirits destroyed in the meat by mana bolt are only disrupted, not toast. Will be back on the job in requisite 28 - force days if free or elementals. Except when nuked in the astral plane from a dual-natured or projecting adversary- in which case they are destroyed.
Its a small change to try and correct a small imbalance. Projecting wizzers get drain in physical and could destroy the spirit with astral combat.
Dual-natured perceiving wizzers get at least one round of very fast astral spirit attacking them while their head is above the parapet, possibale getting Confused by a nature spirit or accident'ed to death.
Advise on improving this would be great dumpshock.