Doesn’t that go against the show core message of change? His Birthdays older self was a swoll Steven but that’s more his Gem shifting him to what he imagines an adult to look like such as how Billy Batson’s Captain Marvel body is based on his idea of manhood, and Steg resembles how Steven drew Greg for the guitar lesson posters.
If anything, swoll Steven represents Steven’s false idea of perfection being presented to satisfy others. Steven isn’t perfect, but a muscular form is all just outward perfection to hide whatever is going on the inside, just like White Diamond did to herself and the Empire as a whole.
Pic unrelated, because I can’t fine the relevant comic where Steven is freaking out and says he’s trying to stay in control because everyone needs him to be perfect to White.