A big problem with talking about whether or not directors are fit for a certain job is that people act like it's a simple thing when it really isn't. We often (myself included) argue points that aren't actually legitimate talking points. It isn't a simple matter of "well that movie he did sucks so this thing he or she does next will suck too" yet this is what the majority rolls with. It's like saying "Vertical Limit sucked, so Casino Royale will suck."
The truth is that there are so many variables that so few of us actually understand because we weren't there or part of the process, yet we argue/debate in circles around it all as if we were. Safety Not Guaranteed was a well-received film with solid writing and direction. Jurassic World was a big summer blockbuster that had been through development hell and back, and the changes we know of that Colin and Derek made to it made the story work a lot better, and they're responsible for arguably one of the most crowd pleasing climaxes in recent memory.
It doesn't really matter what you personally think of Jurassic World when it comes to whether or not Trevorrow is a worthy pick for Episode IX. It's a different studio, different working environment, different circumstance all-around. If you absolutely hated Jurassic World with every fiber of your being, cool, but it's not any indication of how Episode IX will turn out.
