Hmmm... I'm afraid I'm finding the same to be true of my little Queen Arabesque Pleco. She certainly can't cope with my whole 55! I do occasionally wake up in the middle of the night and see (in the moonlight, well, really "streetlight" I guess--I live in NYC) her zooming around the walls of the tank. I think my plec can't manage all the algae in the tank usually. But since I've recently lightened the bioload (heater killed yet another fish even with a heater guard on it!), the algae isn't forming at all.
I'm more a fan of otos recently. Some say the otos only eat algae from plant leaves, but I've seen this not to be true. My guys ate both algae on my plant leaves and the rust algae that was forming in an uncleanable place in my tank (back wall near filter and rock). I do think that, since they are often timid, they need a little extra hiding space, though.