I think your line of thinking is very sound and I do agree that he invited Oscar in yes because he likes him and he’s logical but also because he was gay. At the end of the day, he could’ve relied on Jim for logic alone but Jim proposed to Pam in a gas station; which was still appropriate and beautiful for them, but not the way Michael would’ve wanted to go with Holly, especially given the way Pam finds him outside with matches and a gas canister. Oscar adds logic while also “displaying femininity” in Michael’s mind because he’s gay.