Spoilers just to be safe:
I'd consider that to just be an intended flaw of Dave's that he's too passive. But gets less so as the story goes on and you work through his character arc, especially once you get past day 14.
As for that scene. I don't think he was really expecting Orlando to punch Tyson and seemed a little stunned by it. I mean I wasn't at least. Even then, I don't think that was the time to get defensive over Tyson. The guy deserved some consequence over what he did. Jumping in there would have came off as blindly defending him even when he's in the wrong.
Like as much as he's my favorite character, route, and has my favorite romance, the dude earned that particular L.
Any other time though? Dave better defend his boyfriend. No more abandoning them to fight a killer rabbit alone.