I agree with the OP. I like separating spells by usage. Sure, fireball can be used out of combat to burn something away, but why wouldn't that player just use a torch instead? Also, if a spell can be used as a ritual (like Alarm), why would a caster ever prep it?
Face it: there are a LOT of spells that would never see use in combat. Just let them have their own category the way 4E did it. Rituals are a useful way of categorizing spells by usage. For example, Knock and Tongues would be 4E-style rituals. Shield and Mirror Image are "utility" powers, but are more combat focused.
Perhaps the better distinction would be "combat" and "non-combat?" Shield and Mirror Image are definitely combat spells, but are not about blasting enemies. Maybe we also need a distinction between offensive, defensive, and non-combat?
My reason for liking a built-in way to separate spells is because, without separation, you could definitely have a player that chooses only non-combat spells. Knock, Alarm, Comp Languages, and others are all perfectly valid spell choices. But when the party needs that fireball, how will they react to the answer of "I'm not that kind of wizard?"