Fighters in AI attacks are something like a lull in the storm, but sometimes a deceptive lull: not nearly as dangerous as bombers, and without the missile frigate's "frigate-ing" aoe-immunity and range (both of which serve to let it survive longer in and strike back more at your defenses). But they can still overwhelm you, mow down various unit types on your side, clog up the works, etc.
But yea, anyone dying to a solid-fighter wave is preobably either still figuring out defensive play, still figuring out how to keep AIP down, or lost a big gamble involving AIP and/or raid engines, etc.
To some extent the occurence of fighter waves should theoretically be a breather, in that not everything in the entire galaxy is optimally configured to kill you. (and you can believe as much of that as you like)