Come on, the bolded is just silly. Youth should be supplemented by veterans = young talent is the only priority and everything else is extra. Besides being what I like to call conceptual spaghettification (specifically that youth being supplemented by vets means they are the only priority), it's also a fallacy argument itself in assuming one path to success in NHL team building when there isn't.
There isn't one formula for building a good team. You can have a team of veterans supplemented by youth, or you can have a team of youth supplemented by vets . There are plenty of case studies to this - see the late 2010s Leafs which were supplemented by players such as Tavares and Marleau and Hainsey. Buffalo's problems have been incredibly multifaceted - institutional rot, a market that isn't exactly the most attractive, continued losing (which all leads to the vets they try to bring in wanting out), bad luck (a few bounces go their way in 2022-23 and they supersede Florida for a spot in the playoffs), etc.
Now I don't mind these back and fourth arguments (and that is why I've always assumed you are generally a little more provocative towards me than other posters) but if your retort is that Matthews and Marner and Nylander and co supplemented the vaunted veteran core of Bozak and JVR and Kadri, then I will not bother to reply to you regarding this topic again lol.
This really isn’t an arguable point young teams are bad and older teams are good. It’s a fallacy to expect otherwise. Young players usually are high skill players, but are bad at systems play and don’t contribute to wins as much as their elders. We can prove this without the ability to argue the point really.
8 of the top 10 oldest teams made the playoffs in 2023-24. 0 out of the 10 youngest teams did.
7 out of the 10 oldest teams made the playoffs in 2022-23. 2 out of the 10 youngest teams did.
9 of the 10 oldest teams made the playoffs in 2021-22. 4 of the 10 youngest teams made it.
This list could go for years. How to become a good team is have quality veterans supported by high quality youth. Practically every team who has tried to build around elite youth solely has failed (looking at you Ottawa and Buffalo). This is a measurable, quantifiable fact. You can believe otherwise, but adding elite youth to a veteran core is the sole way to win. The last 7 cups winners, only one is outside the top 10 oldest teams in the league, at a whopping 18th oldest team.
By your own example, Toronto had success because they had the luxury to play Matthews 17:30 a night, Marner 16:45, and Nylander 16:00. Those ranked 7th, 9th, and 15th on their roster respectively. So yes you can downplay the talent they had. But Toronto was good because they had amazing youth that they supported extremely well, and did not put the team on their veritable back despite the great numbers they put up.
You want to know what institutional rot looks like? The only older forward at age Thompson has on the entire team to look up to and learn how to lead a franchise from is Jason Zucker. Dahlin currently has Dennis Gilbert and Connor Clifton as his elder statesman mentors. That’s how perennial terrible teams are made.