Reagents should be used by arcanists. I can see how rangers and druids might be able to be called casters…but largely a druid is simply a nature cleric to me and so should be just like a cleric.
Clerics pray. This idea that there is no fundamental difference between the two types of magic is really troubling to me.
Do mages lose their spellcasting ability if they decide they want to worship a different god on a whim? No. But priests that decide to worship Garagos instead of Lathander are going to discover that their prayers aren't being answered and nothing happens when they ask for a party member to be healed. This is absolute proof that the priest has NO control over 'spells'. They aren't spells. Its a god's whim to answer the prayer of the faithful, and the gods' whims to answer that prayer the way they see fit.
Praying for a heal spell? Tempus would rather see his faithful out on the line, with a huge mace in hand, striking fear into the hearts of the enemy? Suddenly the priest grows stronger and has an aura of fear surrounding him...so has his god commanded, so it shall be.