Yea I don’t think Dahlin dropped off in play really, I was more talking about the spike in production over 2/3 of the 22-23 season that ended up being unsustainable so far. Sounds like Werenski both improved and that improvement forced the coaches to use him in a way that maximizes his abilities, so that makes sense that he could keep this up. You’re right that it’s interesting he’s used the same way for Team USA, when typically national teams will limit defensemen roving since it’s not always needed with elite forwards, unless the player is so good that it’s a better option
They did limit Werenski in the game vs Canada. They were protecting the lead and him and Fox didn't get many shifts. He can play great defense too, but they had McAvoy having a great game and Slavin-Faber is a great shutdown pairing, so I get it. But you're right, in the Sweden game they had Werenski going everywhere and he drove a good chunk of the US offense.
You're right that the roving is not as valuable if he's merely switching places with an elite F covering for him, but he's still breaking the defensive coverage by 1) rotating and wheeling around sowing confusion, and 2) creating odd-man situations with simple speed, where he has the wheels to get back and doesn't need anyone to cover for him.
Werenski has always been a rover since his first games in the NHL - that supposed overly conservative Torts saw a 19 year old rookie and decided to have him go all over the ice and be everywhere. And that's the role he's played with every coach since - some of the systems have been stifling and hurt team production - but every coach has realized the team is best with Werenski trying to do everything.
What really changed is over the summer, largely Werenski's athleticism. We all saw immediately in camp that he looked different. He was just as strong but not as bulky and top heavy. His footspeed was a lot quicker - he was always fast with long slow strides - now he's incredibly fast. He said he learned a lot from training and on-ice sessions with guys like Quinn Hughes, seeing how seriously they take every puck touch, even in the summer. He changed his diet - going mostly paleo I think. And he changed his stick, he was training with Josi and he tried Josi's stick. Zach had been using a very whippy stick since at least his time at Michigan, and with Josi's stick now he has a more responsive touch and can one touch and one time much better. His handling is faster.
Basically what I'm saying is that he's a better player in a lot of striking ways. It's a sustainable change and though his point totals will depend on team effects, his caliber of play is better because he got better.