[Matrixbeast]

I think people find Tusk boring because he doesn't seem to have a personality or any particular traits. He's serious and straight laced, and a little shy, but what do we know about him?
Every comedy needs a straight man, I agree, but Tusk's reactions (Which, keep in mind, for a straight man, are supposed to still be comedic) are just dry looks or stating matter of fact replies. Sela is a much better straight man.
As a foil to Amu and Leo, Yamato and Sela are much better because they have the appropriate reactions to keep comedic flow. His genius is so rarely brought up that the only reason I remember he's the smart one is because he has nothing else to do (Which isn't helped by them showing off that Sela is constantly just as smart as he is). His purpose in the series, as of yet, is kind of overshadowed by Sela.

So far, he's only been notable in episode 1 (When he refused to take Yamato's help), and the Ghost crossover against Meboid Amu. Otherwise, he's just kind of been a tagalong to the rest of the gang, unfortunately.
[Not to say I don't like Tusk. I really enjoy him. But it's easy to make sense why people find him so boring]