Miser = a similar thing, where if you can afford to slowly thin out Copper with Miser, it's good, but sometimes you can't.
It's slow if you only buy one of them, which you shouldn't do if it's a game where Miser is good.
I agree that Hireling has a slowness problem, though. You have to wait a turn, and spend an Action and card slot on it before it actually does anything.
Miser is still slow even if you buy more than one of them. Spending your terminal space on Misers is a real opportunity cost for deckbuilding. The slowness is relative to what else you could be spending those terminals on, not the absolute speed of getting Coppers onto your Tavern mat and getting $ for it.
Edit: to quickly defend Messenger a bit...
Without the on-buy, Messenger would indeed be pretty bad. It would still get picked up for +Buy reasons, but it isn't where you want to be.
The on-buy is the thing that stops Messenger from being bad. Very broadly, in an engine mirror, it's common for players to continually be evaluating trade-offs between buying-that-Village and buying-that-economy, where economy = Silver or terminal Silver or some other thing. You often hit a sort of mini-race, where you're trying to not lose the Village split, but also balance it with picking up economy and other Actions. What Messenger does is let you pick up economy, while making the Village race end faster. It doesn't help you
win the Village split, but it makes it hurt less to detour for economy.
Plus sometimes there's only 1 Action in the pile you're Messengering. You gain first so in that case you get the action for free.
Really the main problem is that the effect is stapled to a Woodcutter-Chancellor.