Thybulle is a good defender but he doesn't strike me as a great one. He's really good at fighting through or around screens and has great hands - which of course is great in the current iteration of the league - but from my limited minutes looks like he struggles in on-the-ball defense, which is also important, particularly given the lack of wing defenders.
(Note, here's a description of Tybulle's and Richardson's defense
from a Philly writer: "And that underscored a point I've brought up several times over the last week: none of Philadelphia's top remaining defenders are true lockdown wing guys, or really anything close. Thybulle and Richardson are too jittery against guys who are capable of blending tempo, transitioning from a move to a counter-move, and finishing from odd angles. The gambling and reaching they do gets exposed in longer stretches against star-level players, and when they have to be the head of the snake defensively.")