For clarity my point is that a world class player does not necessarily improve a team.
When I think of examples of that, I think about Coutinho in Barcelona. It almost seems like a signing they made out of vain, rather then tactical reasons, because he didn't really fit into Valverde's tactic and had to compete with Leo Messi. Also, maybe, Ciro Immobile in Dortmund, who struggled to learn the language and fall out with Thomas Tuchel.
I don't see things going that way for Thiago. He's the kind of midfielder we've been crying for since Alonso or peak Gerrard, and someone Klopp has been a long-time admirer of. He also already made a move from Spain to a much different country, Germany, and proved to be successful there. He knows perfect English and is mature enough, so I don't feel like he will struggle to adapt to the team, coach or country like the above examples.
Of course everything could happen, but if the point you are trying to make is that you shouldn't start world class players in important matches until they pick up form, well, in hindsight, if VVD's first match was of equal importance, would you have started him?