Arguing that sloughing fluid should have more use in order to justify permanent paints is weak at best. Sloughing fluid doesn’t need more use. It doesn’t have to be anything more than a concession for players who want to remove a paint that they hate the look of, but don’t want to wait for the timer to expire. It’s a nicety and nothing more.
Paint is a nothing more than a buff. It operates the same way as armor or potions. Armor degrades with use and potions expire, as does warpaint. It consumes resources, which seems to me is the important point that your suggestion is missing.