I am not going to argue about regression at around 30+ (now 28+ according to some) because it certainly happens. With that said I think this whole narrative that teams rarely win with an older core is less due to regression of the stars but more due to cap issues. Those ~30 yr old stars are always paid much more money than earlier in their career which then affects the depth of team which then affects the secondary scoring which often in turn affects the quality of players those stars play with. And guess what that now affects the stars' production which sometimes could be seen as regression.
Again I'm not saying it doesn't happen...just saying sometimes it could be explained from other reasons. Heck even a less skilled defense could explain "regression" for star forwards because if those dmen can't get the puck to the forwards than obviously they will produce less.
The reason the regression narrative works is because there's an element of truth to it. Players do regress, especially non stars for various reasons. But this isn't the point of the regression narrative.
The point is to support the other narrative that the Avs Cup window will close soon. It's used to support saying the Avs won't be contenders for long, because the players will be too old.
So it's important to point out players that haven't regressed that much in their 30's, and teams that have won with cores of players 29-33 years old.
Also important to note that those who advocated the Cup window closing narrative, agreed with Grubauer that the Avs window would close the year before they won the Cup. Then it was suppose to close with Nate's new contract. It also didn't start because of age, it started because of cap constraints. Now that the Avs have proven they can contend despite those cap restraints, the narrative has shifted to age.
We're past all that now and pretty much everyone agrees the Avs can still win a Cup this year. And the contention window narrative has shifted to closing in a few years. Which is finally closer to the truth, but the regression/contention window narrative is still false, as proven by Tampa Bay almost winning 3 Cups with nearly their entire core 29-33, and Stamkos still playing at a high level at 32/33.
Guys like Kucherov, Crosby, Malkin, Ovechkin, Kane, Panarin, Tavares, Wheeler, Marchand, and Pavelski still playing at a high level in their 30's for that matter too. If they can do it, so can elite players like Nate and Mikko. And the Avs can still win with them in their 30's like Tampa did, especially with the Avs younger blueline with Cale and Bo not even in their prime yet.