No, he wasn't. That's simply not true and never was.
Here are twelve final rankings ahead of the 2015 NHL draft.
2015 NHL draft prospect rankings. Throughout the year we will continue to update our 2015 NHL prospect rankings page with rankings from various NHL draft scouting sites.
www.mynhldraft.com
Just looking at Zboril and Chabot alone they were each ranked in the first round 10 times. (ESPN didn't have either ranked and we can throw out the Central Scouting International scouting list for obvious reasons.)
On those ten lists Chabot was ranked ahead of Zboril 7 out of 10 times.
But again, even if you reversed that
Don Sweeney's entire job is to determine the best player to pick, and he got two teammates playing the same position dramatically wrong.
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Back in 2015, Bob McKenzie was the authority and he compiled his rankings by speaking with all the top scouts and front office people. He was consensus to me and had Zboril 4th and our own Kirk L also had Zboril 4th. But you are correct and I was wrong, the true consensus from that website (a website I use as well) had Zboril as the 6th D.