He had deficiencies in comparison to the other players mentioned, but also had advantages over all of them as well.
Honestly, and I hate to cop out like this, I think he would have closed what little gap there already was with a competent center. Maybe he never is a perennial 100 point guy like those being discussed...he wasn't as good along the wall as Malkin or as physical as Ovechkin, but he was phenomenal at everything having to do with the puck on your stick. He also blossomed into a PK threat and a competent 3 zone player in Jersey.
Look at his career....he scored 52 with Eric Perrin...and that was with Heatley on the other wing, siphoning some chances (rightfully so). When Savard came to Atlanta, they had chemistry, but it was short lived, and he had a prime Hossa on his wing as well, siphoning off some chances (rightfully so). I don't think he suddenly matches Ovechkin's year to year goal production or Malkin's point totals but if the question becomes, would Kovalchuk score 50 on Pittsburgh's second line and 1st PP unit or with Bacskstrom as his center, I'd have to answer Yes to both. Hypothetical, flawed....but yes all the same.
He was incredible. However you feel about him as a player/person, unquestionably, the league is a tad bit worse without him in it. He was that good.