Yes, Duncan is the greatest PF ever. To my mind, the most remarkable thing about him, even more the the titles and awards, is his consistency. The Spurs have a better winning percentage then any other major pro sports team over the past 10 years. They haven't lost more then 30 games in a season since Duncan joined them. They haven't had a decent draft pick in forever, yet somehow every year the Spurs are a title contender. You've seen the Lakers win 3 titles, fall out of the playoffs entirely, then rebuild and win another ring in that same time period.
Stop making excuses for Malones lack of rings by claiming he played in the Jordan era. Malone had Stockton, a top 50 of all time player, Mark Eaton who was twice named DPOY, and a HOF coach in Jerry Sloan. and he could still only manage two finals appearances. It's not Jordans fault that Malone couldn't even make it out of the West.
Sure, the two times he did make the finals the Jazz lost to the Bulls, but even if Malone had won both times he made the finals, he'd still only have half as many rings as Duncan does.
Other contenders for greatest PF
Barkley - No rings
McHale - Not even best player on his own team
Dirk - Great scorer, no defense. No rings.
Garnett - Never able to elevate his team until he joined a couple of all-start with the Celtics.