are gnats that big of a deal for bonsai trees. and if so how do i get rid of them.

They thrive in a soil that is continuously moist. The larva feed on fungi, decaying organic material, and root hairs which will reduce plant vigor.
homeguides.sfgate.com/kill-fungus-gnats-...dish-soap-87288.html
extension.colostate.edu/topic-areas/inse...seplant-pests-5-595/
(look for fungus gnats toward the bottom)

Fungus gnats are not normally a problem, certainly not for healthy trees with a good rootball. They are indicative of wet organic material: Let the substrate dry out longer/further.