I disagree with your timeframe. All of Chychrun, Juolevi, and Sergachev are 3- 5 years away from playing in the NHL. Only top tier kind of d-men, like Hanifin, Ekblad, Jones, Hedman and Doughty have been able to make the jump in 1- 2 years. Hell even R. Murray, Larsson or Pietrangelo took more than what you are suggesting for Sergachev.
And Sergachev is often ranked as the third best d-men in this draft year, a year in which there is no top tier d-men available. Most of the drafting reports on Sergachev don't even list him to be a future top pairing d-men (more like a top 4 if he pans out), and you expect him to start playing top 4??? You apparently see a higher quality in his present and future playing ability than the draft synopsis that I've been seeing on the web.
By way of comparable, is Sergachev the equal of Nurse??? Maybe, but also maybe, probably not??? Well, Nurse spent an extra in junior and should have been in the AHL last year (and without injuries to the lineup he probably would have been), and if the Oilers trade for/ acquire a top 4 d-men or two, and Klefblom etc is healthy, Nurse may start in the AHL for the first half, or more of the upcoming season. That's what one might expect for all of the top 3 d-men in this year's draft.