Absolutely he was. His highlight reel is absurd, but the numbers he put were also pretty mind-boggling for the linemates he had and the era he played in.
On a medium-bad ('mid' as the kids say) 2002-03 Kings team, he had 85 points when the next closest player, an ancient Mathieu Schneider, had 43. The next closest forward had 38 points. So he more than doubled them, while putting up a team-leading +22 (next closest was Frolov's +12). He was really on an island that year, almost unprecedently so, and no one ever talks about that year, ever. And it was very similar when he was with the Islanders. Travis Green, Bryan Smolinski... solid players but not guys who get you to the 90 point plateau without that aforementioned elite talent that Palffy had.
I've made this point before on here, but he had three seasons where he scored in the mid-40s goals-wise. Give him a handful of extra goals, and we're talking about a 3-time 50 goal scorer at the height of the dead puck era and he's got that to hang his hat on.
Ironically, all he had to do was tread water at the end of his career in Pittsburgh and he's probably got the minimum-threshold numbers to have a strong HHOF case. He went out as a PPG player, so with another season or two on Crosby's wing and maybe a decent post-season run we'd have the narrative (accurate or not) about him being a "savvy veteran who showed Sid the ropes when he came into the league". I wrote a hypothetical post on some thread on here a number of years ago where I speculated on what that situation could look like season-by-season. Might dig it up later...