It works well for most players. 5 years will have Sampras and Agassi in one generation, Wilander, Becker and Edberg in another, Lendl and McEnroe in another. Kuerten and Kafelnikov in another. Fed/Roddick/Hewitt in another.
I think it works well for Thiem in with Kei and Milos. Thiem's development curve is not far off from theirs.
There are players that don't fit well into the overall scheme. Where does Verdasco fit? I've had him with Nadal, but lately I think he fits in better with Fed et al. Where does Haas fit? I had him with Fed, but I think he fits better with Kuerten/Kafelnikov.
Thiem is a boundary player, but he's done nothing to really demonstrate why he's an awkward fit for Generation useless. If he starts winning slams and having rivalries with Tsitsipas et al, sure. But we haven't seen that.