Here's what happened with the 3 picks:
1. Zboril -- One of the 3 picks had to be a defenseman and they thought he was the best one and he was the consensus best-defenseman-available. They tried to move up to get Hanifin or Werenski but they couldn't.
2. Debrusk - they wanted a left winger and it was between him and Conner. In hindsight there's no wrong pick but you can see why they loved Debrusk, we all love Debrusk.
3. Senyshyn -- they didn't want another left winger so you look around. I believe they thought Barzal would be a 10-15 goal, 50 assist guy, something like a better version of Spooner. He couldn't put the puck in the net in junior before the draft. And maybe they didn't like something else about him (btw, he's on pace for 10 goals, 60 assists this year) . They would have also looked at Erikson Ek and White but must have decided they wouldn't be good top-six centers in the NHL. So then they looked at RW, which is a position of need in the organization. Svechnikov hasn't panned out and there's the Russian factor. Merkley is still a wild card. Both are also left-shooting right wings. At the same time they fell in love with Senyshyn's upside as a 6-3 scoring winger who could absolutely fly. I'd argue the guy they missed was Brock Boeser who is also a right shot, right wing and would look absolutely deadly with Krejci right now but he was in the USHL and I guess they just didn't see it.
All that said, if you look at Chris Kreider's trajectory, it's similar to Senyshyn. It took him 5 years.