How was Davis a one year rental when he was still in LA 4 years later and allowed them to obtain one of the top 5 players in the league in his prime?
Because the Lakers signed Davis as a UFA in December 2020. This is public knowledge, you can look it up.
Davis wanted out. As did Kareem and so many other players who ended up stars for the Lakers. LA has a huge edge because it's Los Angeles and they have a winning history. That's why they are able to land stars in one sided deals which they have done throughout their history.
Only the Chamberlain deal was one-sided in the Lakers' favor at the time. The Abdul-Jabbar deal didn't quite work out for Milwaukee as they hoped, but they still got 25% of the best players in the first 50 years of franchise history in that deal.
This Davis deal does not fit your story, either, because it didn't happen due to Doncic waiting to go West. It happened because somewhat inexplicably, Harrison believes that Anthony Davis is just about the most desirable player in the league.
You are aguing that Kareem for Brian Winters, Elmore Smith, Junior Bridgeman & David Meyers was a result of the Lakers amazing ability to obtain those 5 players and they were of equal value to Kareem Abdul Jabbar and Walt Wesley. They weren't. Kareem wanted out of a small market and LA was a perfect fit, so the Bucks were forced to trade him for a far less value in return.
Abdul-Jabbar is from New York. Everyone and their uncle assumed the Knicks would acquire him. The Knicks were outbid by the Lakers who had drafted, and were willing to risk, more assets.
In hindsight, we all know that Abdul-Jabbar played 14 more seasons at an incredibly high level. Not many would have predicted that, in '75. Even today, big men do not play at a high level in much of their thirties, and back then, the situation was even more pronounced. Russell retired at 34, and even that was considered very old for a big. Cowens was done at 31. Unseld made his last All-star game at 28. Thurmond's last was at 32, and that was basically only reputational. Elmore Smith's career ended with an injury at 29.
Trading four young, very good, players for ~6 years of Abdul-Jabbar was a big risk.
If Meyers doesn't go crazy and Smith's injury luck is better, and Abdul-Jabbar doesn't turn out to be an alien who can play 'til 42, that trade looks quite good for Milwaukee.