DY: “You haven’t explained why he needs another sevara to be matir a mechalel Shabbos’ pas”
He doesn’t
“If he holds l’maaseh that a mechalel Shabbos has the din of a Yid, he should be matir even if it wasn’t difficult to hire other workers”
He is
You didn’t read it carefully. You are confusing the part regarding non-Jewish workers with Mechalelei Shabbos.
“Where does he state that their halachos are intrinsically different?”
Beginning of 1:46. We forbid a Mechalel Shabbos for wine but not Bishul. The obvious reason is because Mumar may be Menasech but no risk of Chasnus.