What it really boils down to is how good the older players are. For instance, our older players suck for the most part while the Kings' and Blackhawks' older guys are awesome/contribute to Cup wins.
You still need younger guys that contribute
in addition to their core/veterans. It's easy to dismiss this and say "yeah well the GOOD teams don't have to play those younger players because their older players are so good", but you do need young players on ELCs to fill out your roster and actually contribute.
LA: Toffoli, Pearson, Voynov, Clifford, King, Muzzin were all 24 or younger and played at least 24 games during their last cup run, not to mention Doughty. As an added bonus, Muzzin was a 5th round pick for Pitts and we let him walk, and he now plays alongside Doughty on LA's top d-pairing. Blame it on him getting lost in the shuffle when Shero took over, or being a late-bloomer, but either way it's just another example of poor asset management and player assessment.
Chicago: Saad, Shaw, Leddy, Kruger, Frolik all 24 or younger during their cup run, in addition to Toews and Kane (whose newest contracts will force them to continue playing young guys on ELCs, but I digress).
The year we won the cup we were in the same boat: Crosby, Malkin, Staal, Letang, Fleury, Kennedy, Talbot all 24 or younger and played a big part in our postseason.
Same thing is happening this year, the top 5 teams are getting some serious contribution from guys 24 or younger (some more than others):
TB: Stamkos, Drouin, Kucherov, Palat, Hedman, Tyler Johnson, Connolly, Paquette
Montreal: Galchenyuk, Gallagher, Beaulieu, Sekac (before he was traded)
Nashville: Seth Jones, Forsberg, Josi, Ekholm, Jarnkok, Ellis
Anaheim: Gibson, Rakell, Lindholm, Smith-Pelly (traded to Montreal for Sekac, coincidentally), Palmieri, Fowler, Vatanen, Silfverberg, and added Despres at the deadline, who's now giving them 18+ minutes a night.
NYR: JT Miller, Hayes, Fast, Kreider, Stepan
Which brings us to our current roster...
Pitt: Maatta (injured), Despres (traded), Pouliot, Bennett. Of our 4 players 24 or younger to play more than 15 games this season, one had season ending surgery, one was traded, and another seems to be in the team's doghouse and destined to be traded this offseason.
Yes, you need your core guys and veterans to "be awesome and contribute to a Cup win", but they can't do it without help from younger, cheaper teammates.