I love KD - I think over the past dozen years he is second only to Lebron and he had several years where he was the clearly the best player in the league. However, he will be 34 before the start of next season.
The advance stats, especially considering Tatum's defense, have him already better than Durant. And we just saw a first round matchup where Tatum clearly outplayed Durant. He played some of the best defense I have ever seen against KD, all while having a much better offensive series than KD.
It is for sure a debate whether you trade Tatum straight up for KD, IMO. Even if KD is a better player, the age difference alone has to make you pause. And now adding in 2 very important players and 4 firsts and it is an immediate no.
One playoff series does not decide this, and KD had a much worse team around him, but...
TATUM
29.5 points, 4.5 rebounds, 7.3 assists, 1.8 steals, .8 blocks
42% from three
KD
26.3 points, 5.8 rebounds, 6.3 assists, 1 steal, .3 blocks
33% from three