Outdated

It makes sense to me, other than separating divine and arcane casting.
It makes sense for a magic user to cast very lower level spells, at least lowly cantrips, in a subtle manner. Kind of like they've been practiced so extensively and require so little magical energy that the caster could practically do them in their sleep.
Some cantrips already have infinite uses however, so I'm not sure it's a good idea to allow both infinite uses and subtle casting on the same spells/cantrips.