I felt we managed it last season, Sheridan aside (but also don't think it was a failure on his part not to start over the other 2). Even then I think he was a good enough player to start if we had any other striker pairing.
If you're not expecting imports to be first XI players then I think you're aiming far too low.
Expecting imports to be first XI players and an import actually ending up as a first XI player over the course of the season are two completely different things.
I'd say, on average, that across the A-League teams usually get this right 3 out of 5 times. Which is to say imports are lottery and have a good chance of not being as succesful as expected.