Martial and Arcane have more ways to be flexible, "borrow" (especially Wands) and outright recover powers, but they tend to have a lot more support in general.

Divine they kind of tried to bake that in with Channel Divinity at the cost of being more resource-heavy. Holy Symbols similarly have the "no slot, but look how many of them assume you are a Cleric"

Primal on the other hand seemed to go all in on "this is similar but not the same."

And then PHB3 went with "this is not like the others' which leaves Monks and Runepriests in particular to lack synergy with their own sources.