He said that fighting now prevents a devil from losing morale.

The only thing he said about pre-change was that devils only gained morale from casting buffs on you.

Maybe it worked that way pre-change, maybe it didn't. I just don't see anything in Arvam's post that leads to your conclusion.

Actually, if devils weren't working properly before I'd be tempted to assume the opposite: that any new mechanics listed weren't in place before the change.