Were you suggesting that "evil gods don't allow their followers free will" is your headcanon for that, then? 'Cause "no longer playable" implies you're talking about 5e and I don't see anything about that in the 5e MM. In that case, yeah, that's a good way to do things if you want to justify orcs being non-playable and kill-on-sight.
That's pretty similar to how they retconned 5e gnolls, though, and I'd say having two "totally normal savage humanoid that's secretly basically a demon with no conscience or morals" races is at least one such race too many, if not two. If they want to make hyena-like demons and boar-like demons, they should do that, not turn classic races into sorta-kinda-demons and nuke all the relevant lore and history.