But a forward that is drafted number 6 overall is someone you can reasonably predict to be a 20-25 goal scorer and would be doing so for a relatively extended period of time
I don't want to seem argumentative or repetitive, but I think you are very wrong on this. I had a few minutes and took a look at forwards drafted around where we'll pick since 2000. There were 30 total forwards drafted since then in spots 6, 7 and 8 overall. Of those 30 forwards, only 14 have EVER scored 20 goals in a season. The average goals scored per season among those 30 players is 11. Granted it's early for guys like Lindholm and Scheifele, who bring the average down but look to be top 6 players and could have some 20 goal season in them yet.
But then I took out the first 2 NHL seasons each of those guys played, considering they were still adjusting to the NHL and that could be bringing the average down, and even then, only 5 guys drafted at 6,7 or 8 overall averaged at least 20 goals a season in their career- Hartnell, Michalek, Voracek, Skinner and Monahan.
I know this was a crude analysis, but I'll be generous and confidently say that history shows we have, at best, about a 20% chance of drafting a consistent 20 goal scorer with this pick. I don't think Kessel is necessarily the answer to our problems- and I would not add anything significant to an offer- but if we move the pick for him it would not be as bad as some have made it out to be.
Edit: if someone knows how to post tables from excel I'd be happy to post the numbers...