An awful lost of "what if's" and false premises here.
1. If "Rafa is coming," he must not have gotten that memo yesterday. Anyone besides ardent VB'ers can see that a 38 year old pretty blatantly exposed Nadal's age and his drastic decline in movement. Rafa (like Agassi and Fed) cannot defend balls his hard to his FH corner anymore. Fed's footwork and anticipation is better than Nadal, so he masks that deficiency better.
2. "had Rafa proceeded to upset Djoker in the Wimbh final, Rafa would have almost certainly surpassed Fed’s 20 slams."
But he didn't. And the manner in which he lost to Fed will leave a bitter taste in his mouth and ditch his confidence. His chances at the USO are slim, especially since he invariably gets "injured" that time of year.
3. Reaching 22 is unlikely for Rafa.
That's a massive understatement. His chances of reaching 22 are extremely remote. And in your treatise, you don't address that Fed could add to his slam count. Possibly as early as tomorrow.
When even someone as shy and polite as Stefan Edberg addresses Nadal's decline in movement, you know it's bad. He told the BBC, "I retired at 30 and Nadal is 33. He still plays amazing tennis, but he's a lot slower now than even 2017. Today Roger, I think, really exploited this, which is interesting since he's 5 years older than Rafa."
Finally, Fed doesn't have to do anything to "secure" his legacy. You act as if by some miracle he's passed in the slam race, his "legacy" becomes an afterthought. If Nadal retires with 18 total slams, is his legacy a poor one? Borg has 11 slams, he's a legend of the game.