Yeah, even dashing, it should take a little less than two full rounds to reach the top of a 50 foot rope (which is what comes standard in most adventuring kits), so the character should have had plenty of time to see that the monsters were following him up the rope and maybe realize this was a bad idea though.
More importantly though, the “metagaming power move” thing is a red flag. It sounds like you didn’t like the player’s use of that tactic for some reason and instead of talking to them about it, decided to punish their character for it. That’s generally poor form. There’s nothing wrong with casting rope trick during combat, just like there’s nothing wrong with the monsters following you up the rope. Both are perfectly valid actions the characters involved might reasonably take. Yet both parties seem to have been upset, which speaks to a misalignment of expectations. You need to talk to this player openly and honestly about what happened so you can get back on the same page.