Lidstrom won back-to-back Cups with Detroit when Yzerman, Shanahan, Federov, Konstantinov, etc. were the "core" in Detroit. Four years later he won one when Hull, Robataille, and Chelios had replaced previous core guys. Then he won another five years later age 37 when most of the second wave of guys were gone and the team core was now Datsyuk, Zetterberg, Rafalski, Franzen, etc.
I'm trying to illustrate two points with that information. First is that the notion of correlating a specific group of players with a specific competitive window can be an unnecessarily limiting perspective. A good organization can orchestrate an extended run of competitive success that far exceeds the peak years of a handful of their best players, provided that they draft and manage their assets well to maintain a steady influx of talent. It's important to realize that sacrificing the future while chasing the peak years of a specific handful of players can actually be a counter-productive mindset for an organization.
The second is that age shouldn't really be a consideration for whether a player is part of the core or not. Moving on from Lidstrom just because he was hitting his mid-30s when Datsyuk and Zetterberg were hitting their primes would have been a huge mistake. You're part of the core as long as you're filling a necessary role at a high level, regardless of age. Having all your best players hitting their primes together is definitely not a prerequisite for winning.
If Thomas can step in and fill a role at a high level while those other guys are around and doing the same, then I'd say he's part of the current competitive core. If this year's play is any indication, he has a pretty decent chance of doing just that.
