I think that Filler struggles psychologically with two things: elite players who are his age or younger (Gorst, Kaci), and players who are slower and more methodical, while also playing just as good as him (Gorst and Kaci again, as well as Albin Ouschan).
On the flip side, I think he has zero fear of guys like SVB, Shaw, Chang, etc. They are older than him and in his eyes, he does everything they do, but better. He seems to relish beating those guys.
But as Jaden said, I could see his edge starting to diminish a bit as he ages. First from the realization that he's not invincible, and second from losing the "boy wonder" aura. Filler is an old man compared to Gorst's 22 years of age. But the Filler/Kaci/Gorst crop of young elite players isn't the last, and it won't be long until they're late 20s/early 30s facing off against kids in their teens/early 20s who play just as good, if not better, than them.
I think the current crop of young players grew up being influenced by SVB (who along with Earl and Efren was the game's first internet/YouTube celebrity), and soon we will see a crop of players influenced by the likes of Filler, Kaci, and Gorst.