The benefit of Eichel is that at 24, he fits the timeline of the team better than Zibanejad. Let's say that the team continues to show overall improvement as the young players improve. Next year, we could be a bubble team that makes it in. The following year, we could be a team that makes the playoffs comfortably and wins a round or two. The year after that, we start to look like contenders. At that point, Zibanejad is 31 and likely has a hefty cap hit, declining production, and 3-4 years left on his contract. While Eichel would be 27 with 3 years remaining on his current contract. The team would be hitting their Cup contention years at the same time as their 1C's prime years.
Does this scenario have issues? Of course it does. Eichel will be expensive to trade for. We will almost certainly have to move Buchnevich, Zibanejad, and Strome in other deals either in this offseason or over the course of next year. If Chytil is in the trade, then that opens a big hole behind Eichel. We would have to look for a young 3C that could move up to 2C the following season in the return(s) for Buchnevich, Zibanejad, or Strome.
What's the alternative? We resign Zibanejad and hope he maintains a high level of production from ages 31-34 and that the contract doesn't become an albatross. Or that he maintains a level that is just good enough to center our (hopefully) top flight wingers. And that Chytil progresses to the point where he is the 1C during the Cup contention years, or at least a 1B to to Zibanejad's 1A.