I agree he'll be pretty strong but Sabo was above his pay-grade. With a good fruit, he could prove to be a formidable opponent.
I have either him, Pizzaro or the 10th Titanic Captain facing Sanji so I expect a lot from him if Oda goes that route. I also don't think his performance so far has been irredeemable, him appearing in Dressorsa to get Ace's fruit and being one the first members of the crew atleast suggests he may end up important.