Again, Isles would trade those prospects, but won't be sending you two 1st round picks along with ONE of them.
Droiun was just traded for ONE elite prospect. Why should the Isles offer more than that?
A) because Duchene is a Center, unlike Drouin, and so holds quite a bit more value
B) because Duchene is a Center who has become an elite faceoff guy and strong two-way player; though Drouin's two-way play is often under-rated, there is a significant gap to Duchene's. Plus Duchene is bigger and a lot stronger with a power game...that Drouin will never be able to develop...to go with speed/skill game that both broke into the league playing; which has helped turn Duchene into a much better goal scorer, even though Drouin may be even more dynamic & versatile as a playmaker.
C) because Duchene has hit levels in the NHL that Drouin has yet to scratch with any sort of consistency. So it's not unreasonable for a GM to think that him returning to those levels on a functional team, with a fresh start, is a safer bet than Drouin continuing to progress in his development towards the exceptional upside he has.
and finally; D) because Barzal is the only one of those prospect with similar value to a bluechip defensive prospect like Sergachev. Which is also why you'll find that if Barzal is the prospect, a lot more avs fans would be content with only one of the 1sts and a 2nd, while being willing to retain on Duchene & take a cap dump...at least amongst those of us who are open to package that do not include a potential #1 LHD.
Beauvillier, Ho Sang, and Sorokin are really exciting A-prospects, but none of them is a bluechip Center or Dman; that really is the crux of it. Star goalies don't have anywhere near the value of star Centers or Dmen, just like Starting goalies don't have the value of star Cs & Ds, and the same is true of bluechip goalie prospects...especially ones who's desire to play in NA is in question. And though I love Beauvillier and would love to have him joining any of our future duos up front (MacK & Mikko | Landy & Jost | Greer & Compher) he isn't a bluechip top line C either; same for ho sang. Those are sweet prospects that it would be nice to get our hands on; but they don't hold the value that your Sergachev or Barzal or Dubois's do.