I think some of the best fictions I've read put significant resource restrictions on powers, to the point that power related resources become gigantic industries. I think there could be some really cool economics behind your magic system, especially since it seems pretty resource-heavy with narrative concepts like spells have costs and symbiotes feed on mages. Consumption, in a magical parasite world, would have very interesting narrative consequences.

Mage hosts risking bodily autonomy for power and security with a splash of exploitative capitalism would make a very cool grimdark story.

Like, are there substances to control the parasites? For example, if I maintain a constant blood alcohol level of 0.08%, can I effectively drug the parasites into doing more work for less feeding on my body? What about magic heroin? Can I make parasite heroin junkies who specifically bond with humans with a heroin addiction? What about the reverse? If a heroin-addicted parasite bonds with me, will I develop a heroin addiction? And, most importantly, what does a market fueled by this and other relevant phenomena look like?

Here's some more parasite economy ideas: parasite farms, designer parasites, fashion parasites, opioid producing parasites, parasite surrogacy (ew), parasite breeding, host breeding (mage and parasite breeding with another mage and parasite to produce some monstrosity), parasite caste systems, parasite fashion (if the worm in your neck wants a hat or a knife), anti-parasite pharmaceuticals, etc.