What does that good mean? I think it can be argued he was good before he had an amazing half season, statistically, last season, I think Ellis took longer to develop than many thought but since he has been in the league I've seen a steady improvement every year. It's not atypical for defenseman not to hit their peak until their mid to late twenties. I think he has developed differently than expected but at the same time has developed as well as you could hope for. By that I mean he isn't the defensively challenged small offensive dynamo that was expected. Instead he became a steady defenseman whose size and skating didn't hurt him as much as expected. To counter that he also didn't become the offensive dynamo from the back end.
Last year in his 44 games he was on a roughly 17/18 goal 60 point pace. I'd agree he is not that good. If he was that good we wouldn't be getting him at 6.25 no matter the term. If he can settle into a 10-15 goal 40-45 point steady defenseman this contract is a win.
I agree about the durability but any player you sign for that long is a risk. I also agree the big win is no NMC/NTC. Poile has done a great job of building a SC contender, locking core guys down to good contracts but also keeping his options open for the future when the situation will inevitably change.