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Bug is the most interesting and flawed type in Pokemon...
Pocket monsters were inspired from the activity of bug caching as a kid; running around with a net, collecting, exploring the forest and so on. Bugs are the heart and soul of Pokemon. Try to imagine all of them being removed and you quickly see why that is so.
Bugs are strong relative to their size, but most of all, they have short lifespans, make up most of animal life in biomass (and cerrainly individuals) and are usually either hard to catch, see, or too phobia-inducing to be approached. Many people are also deathly allergic to their venoms (some with wasps, all with the black widow).
So bugs need to evolve and be strong fast, but retain certain advantages late game, appropriately either through high speed, evasion, or status afflictions.