You said the sentence "depth is pretty much always better than a great line". I'm refuting that claim. Having a great line is infinitely more important than depth. The year the Sharks got the furthest was the year where they possessed the single best line in the entire NHL. I'm not so sure you're helping your cause by using the Sharks as an example.
And hello? The 2017 Pittsburgh Penguins had HORRIBLE depth. They had the four leading scorers in the playoffs (Malkin, Crosby, Kessel, and Guentzel) and then their next leading scorer up front was Chris ****ing Kunitz with 11 points in 20 games. Their defense consisted of Justin Schultz, Ian Cole, Ron Hainsey, Olli Maatta, Brian Dumoulin, and Trevor Daley.
It's funny that you ask me to name Cup-winning teams without great depth, because I could ask you to name a Cup-winning team without multiple superstars. The 2017 Penguins won with horrific depth. There is not a single team that has won without multiple superstars/an elite first line. It's rare but possible to win without depth. It is impossible to win without superstars.
You talk about how Hertl/Meier or whoever has improved since 2016 but you fail to consider who is worse. Vlasic is worse. Braun is MUCH worse. Those two were the pillars on D in 2016, they were downright perfect. They have both declined visibly since then. Couture had a playoff for the history books in 2016, he's not going to repeat that. Suggesting that Pavelski this year is better than the Pavelski of the first three rounds in 2016 is recency bias at its finest. Never mind Burns. So yeah, the depth has improved. But the stars have declined.
If this year's Sharks go to the Stanley Cup Finals, then you can just "let me be wrong".
Until then, the 2016 Sharks were the best Sharks in team history and it's not close.