It's a massive win/win for both sides. Pelicans get an unprecedented haul for an expiring contract. Lakers position themselves to have a Big 3 of LeBron/Davis/Kemba (or Butler or Kyrie)... Lakers should be the frontrunners to win a title and the Pelicans will have one of the most exciting young teams in the league.
I didn't see us outbidding that offer without giving up Tatum, Brown, Smart, #14, #20, #22, and the Memphis 1st - and that wasn't going to happen without Davis agreeing to stay long term and Kyrie agreeing to re-sign long term.
As far as the Celtics concerned - they are about to step into irrelevance, but it'll be fun to watch Tatum develop over the next several years.