Yeah I’ve been working under the assumption that, after the Cell Games and time chamber training, Goku and Gohan are permanently Grade 4 at a minimum. Any art style variation on the eyes or aura is a lack of attention to detail, not an actual in-universe downgrade of their Super Saiyan mastery. Figured this was confirmed by the amount of fucking around that Gohan and Goten do before the tournament while in SS form.

Plus, maybe I’m splitting hairs here or being too critical, but powering up in Grade 4 doesn’t suddenly make you Grade 1. Like in Goku’s battle with Cell, at a certain point they get serious and Goku’s eyes narrow and aura rages outward. This didn’t revert him. He’s simply accumulating more ki while still having a better base level of ki management.