I don't agree with Forretress. Its Bug Bite attack(the only good Bug Type attack it can get of his moveset) is very good. Its low speed gives its Gyro Ball attack massive power towards fast opponents.
It sets out good entry hazards like Spikes and Stealth Rock. Its very sturdy with Defense, good with Attack along with its Light Screen and Reflect walls. Vibrava doesn't make much a difference if you replaced it. You should've kept Forretress and don't judge it for its Speed and learnset when you got a powerhouse.
Ariados isn't that bad considering the learnset and stats. Yes Swoobat is annoying and useless and the others you mentioned.