Tavares at 28 years old will only been good enough to get you to a wildcard playoff spot in the short term. Long term he turns into a compliance buyout. You need young superstars in this league the win now. Any team that says they are rebuilding and doesn't go all in on Jack Hughes is lying.
I get where you're coming from, but I think you undersell Tavares a whole lot in this. If Tavares stays healthy, he is pretty much the most likely free agent to be worth a gamble of any free agent since like... Hossa. What young superstars does Pittsburgh have? Last I checked, Crosby, Malkin, and Kessel are all around 30. I'm not trying to say that Tavares is on the same level as Crosby or Malkin, but he is one of the best forwards in the NHL right now.
Look at Jason Spezza. I would argue that Tavares is going to continue to be a better player the next 5 years than Spezza has been moving from Ottawa to Dallas. Regardless, Spezza is a former top pick, he's 34, and just now he is putting together his first really mediocre season of his career. If the risk of signing Tavares long term is that he's going to be 34 and finally dropping into really unacceptable production, I go for him 10 times out of 10.
I agree, the NHL continues to develop towards being more of a young, speedy game. I also think that you have to factor in just how good a superstar player can be for a team. On the flipside of the young superstar argument, McDavid and Eichel are both insanely good players but neither have been able to really push their teams' into perennial contender status just yet.
Adding Tavares alone isn't going to win you a Stanley Cup. However, if Larkin and Mantha continue developing, the Wings use their 2018 1st round pick to snag a really good defenseman that can help sometime in the next couple of years, they hit on another trade/free agent, Hronek/other dmen hit the NHL... you're looking at a team that could compete. It's hard to say because you don't see this sort of thing happen often anymore, but if you get a guy like Tavares, and find a way to surround him with some talent, your team is going to compete.