I'll ignore the awful trade idea and focus on the Leonard vs. Davis:
Leonard 100%, final answer. Davis looks like he could turn into an MVP candidate someday, but Leonard already is one and has great playoff experience. He's the best 2-way player in the league and the perfect player for defending both Lebron and Durant. You put him on the current team (minus rookies/picks) and we would be the favorites in the east, with a good chance at unseating GSW as well
Edit: That said, he should not and will not be traded
So what type of offer works then?
Pelicans and Spurs wont let these players go easily. Overpayment is likely in order
The issue is that you didn't overpay. Like, at all. Signing and trading a player is not the same as trading them. It requires the other player to want to go there and the other team to come to an agreement with them on salary (aka enough for them to just sign the player without giving up an AD or a Kawhi). For this trade to even remotely make sense, you'd need to take out IT and throw in the Nets pick at a minimum (and likely the LAL pick as well), plus Crowder and/or Morris to match salaries. You may be able to take out either Tatum or Brown in that case, but one will still be there.
Not only that, but why would we trade IT in an all-in move like trading all our future assets for Kawhi/AD? Smart certaiy isn't ready to take over, and we'd have zero cap space, so how would we win with that team?
You cant have maxed out horford, hayward, IT4 and Leonard or Davis moving fwd
And yes the opposing teams would entertain a sign and trade bc IT4 is a good talent plus they get Tatum and Brown in return
The uncertainty as to where the 2018/2019 picks land wont do the trick. Higher risk for Pelicans/Spurs
I would be on the fence .... Hate to give up tatum and brown but if IT4 is no longer in the Celts future plans but pelicans/spurs want to rebuild... Need to think about it
Hayward plus leonard alone would be a deadly 1 2 punch