Davis was going to get traded the summer he did. There is absolutely no guarantee he ends up in LA the following year as he may have actually liked whatever team traded for him. Remember when everyone said Paul George was going to go to the Lakers in free agency and then he re-signed in Oklahoma City because he actually liked it there (and they could give him more money). Maybe Davis would have ended up in LA, but maybe he wouldn't have. Secondly, as we all know Lebron is old and on the downslope. By waiting a year, you waste whatever time you have left of Lebron. There was certainly no guarantee that Lebron would still be a good enough had they waited a year. It turns out Lebron still would have had enough left, but that was far from a given. I mean plenty of this board basically wrote Lebron off when he went to LA. And then his first year there, he suffered the first major injury of his career and the Lakers missed the playoffs entirely. When you have a guy like Lebron, you don't wait and rely on chance. You go all in and try to maximize your title chances. The Lakers did that and actually won a title.
Last summer was the disaster. By most accounts they easily could have had DeRozan or Hield instead of Westbrook (they would have been able to keep KCP or Harrell as well - Kuzma was gone in the trade in all 3). They let guys like Caruso, Drummond, and Schroder go because they didn't want to pay as much in luxury tax. They could have had a vastly different roster had they not gone all in for Westbrook.
I mean how much better is this team then the one they have now
PG - Schroder, Caruso, Rondo
SG - Hield, KCP, Bradley, Reaves
SF - James, THT, Matthews
PF - Davis, Anthony
C - Drummond, Howard, Jordan
Plenty of blame to go around in LA land, but it seems the biggest impediment was Jeanie Buss getting cheap and the pursuit of Westbrook instead of
a better fitting player like Hield (which most everyone including Pelinka and James thought was the better option and obviously didn't work out like they thought it would).