there should be a rule where if a player doesn't move in 2:30 then they automatically lose.
I don't mind an opponent who uses the clock anyway they want to in rapid...that is the point of a clock. What I hate is VACATION ABUSE in Daily games. People who use vacation mode to avoid making a move. Chess.com...PLEASE allow NO VACATION MATCHES!!
Yeah, I actually have something similar to that going on right now. It's not vacation time, but the guy, I'm pretty sure, is purposefully waiting until the last possible minute to make every move. It's a 3 day game, so he will only make a move every 3 days, even tho I notice that he has been on many times earlier than that. This may not be as bad as what you are describing, but it's really slow. I also noticed that the majority of his wins were wins on time or players who resigned perfectly fine positions. So, I suspect that he just continually grinds out his games this way and gets people to give up because he plays so slow.