Physical bugs certainly weren’t doing well either — Gen 4 in general set about the task of “filling in holes” in type movesets; giving them good solid moves most of the type could learn when previously there were shaky options at best, and also done this in light of the new special split. Bug Buzz, X-scissor, Energy Ball, Seed Bomb, Iron Head, Flash Cannon, Poison Jab, Air Slash, Dragon Pulse, Psycho Cut... it was practically Gen 4’s big thing when it came to introduced moves. Most every type now had a leg to stand on with reliable, accurate, powerful moves; both special and physical, with most having very good distribution among their type and most especially those who needed it. Except Flareon.If nothing else, bugs buzzing generally does pretty good psychological damage to people who hear them. Bees? Mosquitos (or flies)? Cicadas? All are, at the very least, annoying, or possibly indicative of a sting or other sort of threat.
That's a fair point of a lack of good special Bug moves going into Gen 4, though physical was honestly lacking more if you took Megahorn out of the equation (and it didn't really get much Bug rep aside from Heracross). Special at least had Silver Wind and Signal Beam; though weaker, they were stronger than the other physical Bug moves.
It might just have been the worst thing to happen to types in my opinion but that’s an opinion for another day.