What this boils down to is would it have been smart to trade the #1 pick in 2017 for the #13 and #14 that year instead of the #3 and a future (that ended up being #14). In general, that kind of a trade would not be a very good trade for the team giving up the #1 pick. There are years, such as when Wiggins ended up being the #1 but in general, no. And certainly not when you compare #3 and a future that was expected to be really good to getting #13 and #14, no one would take the latter given the chance for the former.
To go total hindsight and say would you today trade Tatum and Langford for Mitchell and Adebayo, that is still a tough one. Mitchell is really good but is he Tatum good? Adebayo is really good at the hardest position to find a good player at. I think I would make that trade though. It defies the conventional wisdom of never wanting to give up the best player but in this case, you are getting two really good players so I think you do it.
There has been a lot of talk about trading for Beal. Most people say that they would not trade Tatum for Beal. Is Mitchell better than Beal? Maybe, and if not, he is pretty close. I think WAS would be pretty happy to get Mitchell and Adebayo for Beal, and they should be. Tatum is more than Beal but this is still a good trade (albeit totally unrealistic).