I'm gonna say Inglis. Had a couple of years at Storm where he was immense, and often lifted for QLD, but in his Souths days, I feel like he spent the vast majority of the time just going through the motions, with the odd moment of athletic brilliance.
Had all the physical prowess to dominate week after week, but just never did - partly due to his body not being able to keep it up, partly by being a tad lazy...
Gets spoken about as a potential future immortal, but IMO, he wasn't at his best, consistently, for long enough.