Yeah, I mostly agree with you but I should say these comparisons between Fed and Alcaraz aren't really accounting for matchup in style. Djokovic's level of play is frankly stunning at his age and there's obviously some luck that his body has held up. But Fed playing Agassi is a bit different from Alcaraz playing Djokovic. Djokovic is a counterpuncher/grinder and probably the best ever with this style. And it's the same style that's the worst matchup for a young aggressive player who can sometimes lack patience. Aggressive players always struggle against Djokovic style players until they hone their discipline and strategy. It's the same reason Chang dominated Sampras early on before Sampras got it together and blew him away. Not to say Alcaraz or anyone is capable of blowing Djokovic away but it's a similar situation. Fed v. Agassi on the other hand, doesn't present any real matchup problems for Fed. Agassi was slow and while he could pressure Fed with his ball striking, Fed could beat him mostly playing his own game, save for playing a bit more patience.
Guys like Alcaraz who have lots of tools always takes awhile to figure out how and when to use each weapon. For Fed, it was focusing on serve and forehand, coming to the net less and being more selective about when to go for a backhand. For Sampras, it was also about being more defensive on the backhand and relying more on serve and being selectively aggressive, waiting for a forehand that he can unload on. Even when Sampras missed on the FH, it scared the sh-- out of the other guy so he was able to intimidate. As for Alcaraz, I don't know. Maybe grind a bit more, rely on his speed, change speeds on forehands so that they look even bigger when he goes for them? I do notice Alcaraz does not as often do what Nadal used to when falling behind in a rally- Nadal would put some air under the ball to give himself more time to get back into position. Alcaraz often just unloads, which is great if it becomes a running winner but gives him less time to get in position if the other guy returns the shot.