Laughton and even Hartman are guys you squeeze knowing that we should be replacing them in 1-2 years max. Every penny saved on them, gives you more to spend on your upper tier guys.
I'm going to disagree with you on Hartman. He's already looking like the most dynamic bottom-sixer we've had in years. When you have a guy who hits, is fast, is defensively responsible and puts in 15 goals a year, there's not really any reason to replace him. Move him to the fourth line if you will, but you can keep a guy like that on the roster till he's 30. Kinda like Darren Helm on the Red Wings, except Detroit kept him probably 3 years too long.
As for Laughton, somehow he's gone from "the only guy on the team playing to his potential every night" to "meh." I think Hextall and Hakstol really messed with him. There was a time when the story of Laughton being banished to the minors served as a cautionary tale for other young Flyers prospects and was somehow viewed as a triumph of the Hextall process.
Was it really necessary? That was the year of TK and Ghost being benched, Bellemare and VdV playing 82 and 81 games. Couldn't he have been with the big club, learning how to play defense and still contributing more than Dale Weise or Lubimov? He's a guy who honestly would have been better off going to Vegas in the ED and they'd probably just let him play, and he'd be a better player for it.
Laughton is definitely replaceable but he serves a lot of roles. If he's still here in 2 years it means that our highly talented deep talent pool failed somewhere, management did a terrible job of sorting through the talent, or Laughton took some huge step forward. I don't think those things are likely; I suspect Rubtsov has a better chance of being a lineup regular than him by 2021.