Do caster out of combat options matter?

[Aimeryan]

I am skeptical of the claim that you need to DM by proxy if you don't have certain spells, and I'm afraid the only solution we have here is to start throwing out examples and arguing over those examples.

I'm also skeptical that players don't have agency without certain spells.

Not no agency, less. I acknowledge your skepticism, however, the fact of the matter is that the skill system - as well as exploration in general - is highly DM fiat. Something the player may think will work can fall down at a dozen points with a casual remark from the DM. Spells, on the other hand, do what they say they do.