TwoSix
Everyone's literal second-favorite poster
While I can't debate the value judgment of "should be a valid playstyle," I think it's telling that there are virtually no offensive buffs in the Basic set, and the few that exist are all concentration.Self-buffing on casters still should be a valid playstyle, especially for all the types of casters who can fight with weapons reliably.
As another example, the eldritch knight subclass for fighters can only cast wizard abjurations and evocations, so not a lot of buffing outside of reactive buffs like shield.