Jeez, McHale is being underrated here, in my opinion. I wasn't alive when he played, but from what I've read, and from what I've watched, the guy was a monster on the block, arguably the best post player ever. If his feet don't give out, the guy probably could've played into his forties.
Duncan is better than KG. For starters, he has more rings. Second, he could play any style. He won two titles during the era when defense beats offense, he won another title during the era where the league was adjusting to new rules, and he won another when the league became offense, small ball oriented. Even today, he is performing at an incredibly high on a team that has consistently won year after year after year. Finally, he could adapt to any game or situation. If the Spurs needed 30 points, he'd do it. If they needed 20 rebounds, he'd do it. If they needed him to play defense and do the dirty work, he'd do it. I don't think the same could be said for KG (just personal opinion).
KG is all-time great. I love the guy, and he probably became the first guy who was an elite player that was a jump shooting big. I'd go as far to say there's no Kevin Durant game today if it weren't for KG. His defense and intensity are characteristics I'll always appreciate.
Malone is one of those guys who did great things, but in the end left you wanting more. I'm a firm believer that if he wasn't so scared in the clutch, those Jazz teams could have knocked off the Bulls. He was the best running big man ever, one of the most well conditioned players ever, and his PNR game with Stockton was one of the most unstoppable plays ever.
Nowitzki probably did the most globally out of all these PFs. After winning the title, his fame skyrocketed across the world, even after being loved worldwide, especially in Europe. I'd also venture to say his championship was the most improbable out of any of these PFs. Against the Blazers, everyone thought Dallas would choke, because they always did (and they collapsed in the Brandon Roy Game 4 masterpiece). But they pulled it out, and then SWEPT the defending champs, without HCA. That is impressive in itself. Then, Dirk single-handedly destroyed the Thunder, and capped off the playoff run by humiliating the Heat.
All that being said, my list goes like this:
Duncan
McHale
Garnett/Malone (it could really go either way)
Nowitzki
McHale rightfully loses points for his lack of longevity, which imo is a huge thing to look at when considering all time greats.
I dont really get your point about his feet. Yeah if no one got injured or aged they could play until they're 40
It's impossible for people to not age. It is possible for people to have healthy careers.
Strongly disagree about all players being able to pay in to their forties if they stayed healthy.
For example, look at Rondo. Even if that injury never happens, he still wouldn't last that long in the league (maybe until he's 34 or 35) unless he changes his game. Whenever a person a ages (especially athletes), they tend to lose athleticism, right? Rondo, a guy who relies heavily on athleticism, would be a significantly worse player in his later years. You know why Kidd is still playing? Because he can pass and shoot. If he still couldn't shoot, I'd argue he'd be out of the league. Same goes for Rondo. That's why this injury scares me so much. If Rondo loses a chunk of athleticism, he'll never be the great player he has the potential to be.
The reason a guy like McHale could play into his forties is because the way he played would've been unstoppable, whether he was 20 or 40. His endless array of post moves worked on anybody from when he entered the league to when he was forced to leave it. What makes you think those moves wouldn't have worked past that time. I'd bet they would.
And lack of longevity? Well, then I'd argue KG loses points there. The guy has a freaking minutes restriction for crying out loud. Yeah, the argument could be made that he has that because he injured his knee, but then why can't I use that argument for McHale? It goes both ways.
KG is in his 18th season. McHale was in the HOF 18 years after he started playing professionally.
Did KG go to college for four years?
Would KG have a ring had he not been traded?
Could KG have been the outright best player on a championship team?
The answer to those questions is no.
I think even if McHale hadn't been on the Celtics, he could've been a champion, if he played with a great second banana (like a Wade to LeBron). Was KG our best player in 2008? Probably. But it was close. Pierce played at an unreal level all year, and then took it to another level in the postseason. And going by his years in Minnesota, he couldn't get it done. Even the year he had a great supporting cast (Cassell and Sprewell), he still couldn't get it done. Now, I think Cassell got hurt, but shouldn't that mean the star steps it up?
Edit: in response to your edit:
McHale was a great defender; McHale was as good a rebounder as KG; while not being near the athlete KG was and is; McHale has an elite jump shot that you had to respect.