Let's look at the physical requirements of Pierce and Nowitzki's games:
Nowitzki: No mobility required at all. Thrives from 3 point spot ups and turn around jumpers.
Pierce: Like Chauncey Billups, mostly just good at making it look like he's been fouled. He is a flopper and is extremely intelligent at predicting what a defender is going to do and putting some body parts in the way of that defender. He is also a very unselfish player whose been able to create value for his team with his excellent court vision. Lastly, Pierce has always been good at getting under players' skin with his defense. He is a student of the game who understands players' play styles and uses that to give them a hard time.
Melo's game is predicated on three things: Strength, quickness, shooting ability, which combine to make him great at creating his own shot. If he can no longer create his own shot at the efficiency he has in the past, what's left over is a good 3 point shooter, which is not worth $25m/year. What happens when Melo slows down, which is inevitable for older players? Suddenly, defenders can play him closer because they're not worried about him going around them. His step backs are now better defended. He draws fewer fouls. His efficiency as a go to scorer drops. That's a fact of nature, and if you go and look at the full list of stars over the last decade, you'll see that by about 32 years old 95% of players who bear any resemblance to Melo are in decline.
Now let's talk about how you win a title. The answer is simple: you get more talent per dollar than other teams. Let's look at some of the best teams in the league and how much value they get for something near the $23m Melo will make next season:
Golden State: Curry ($10.6m), Thompson ($4.1m), Draymond Green ($0.9m), Harrison Barnes ($3.0m), Marreese Speights ($3.7m). Total: $22.3m.
Hawks: Horford ($12m), Millsap ($9.5m), Korver ($6.3m). Total: $27.8m
Grizzlies: Gasol ($15.8m), Conley ($9.3m). Total : $25.1m
Blazers: Lillard ($3.3m), Matthews ($7.2m), Batum ($11.8m). Total: $22.3m
Houston: Harden ($14.7m), T. Jones ($1.7m), Motiejunas ($1.7m), Josh Smith ($2.1m), Patrick Beverley ($1m). Total: $21.2m
OKC: Westbrook ($15.7m), Ibaka ($12.3m). Total: $28m
SAS: Parker ($12.5m), Duncan ($10.4m), Leonard ($2.9m). Total: $25.8m
Would any of these teams trade these players on the list for Melo? No. THey'd all laugh. Because these players all provide significantly more value per $ than Melo, which means as good as Melo is, his salary is so big that it's not a great value.
And that's how you win a title: getting great value. Imagine you are at a blackjack table with altered rules: there are 30 players, and only the player closest to 21 wins the pot (it splits for ties). Now all the sudden you have to hit on pretty much anything because one of those players will get 21.
It's the exact same scenario in the NBA. You have to take wild risks because the only way you win a title is if your team is better (or slightly worse and lucky) than all 29 other teams. That means that unless you already are close to being a title contender, you should not care at all about the fact that certain moves have a chance of not panning out. Your entire focus should be on the question, "How good can we be if these moves pan out?" Because the only way you win a title is if you go for max potential and end up getting lucky.
You have to hit, even if you're on at 19. Keeping Melo is kind of like sticking at 14.