Players 25-and-under many people would take before Eichel (YMMV), listed in order of points per game since 2015-16:
Some might be interested in a D-man instead:
Or even a goalie, such as Matt Murray. That's 20 names for which an argument can be made that they're better players than Eichel. I'm not making that argument about all these guys, just outlining that Eichel is not legitimately one of the top 2 / 3 players in his age group by any metric. He's a good player and I'm glad Buffalo has him locked up for 9 more years, I just don't think he's worth Patrick Kane money.
Was Patrick Kane worth his contract?
Over their first 3 years...
Kane - .31 goals per game, .63 assists per game, .94 goals per game
Eichel - .35 goals per game, .50 assists per game, .85 goals per game
Not all that dissimilar. And factor in that Eichel has played on a bottom-dwelling team his whole career while Patrick Kane was on a team that won the Stanley Cup in his 3rd season.
My point was not that Eichel had a better season than some of these other guys (Kucherov, etc.), but he IS a better talent and has more promise, which is important since what we're discussing is in the context of a long term contract.