>>55529469That's the tier list for real Pokemon (singles). Defense is a lot more important in real Pokemon because you can't just double into one Pokemon like in alt formats like Doubles or Triples. Bug's resistance to Ground and Fighting, 2 of the top 3 attacking types in the game, gives it a very valuable niche, especially when paired with Bug types universally getting STAB U-turn. Offensively it's underpowered due to all of those types that resist Bug, but Bug is still one of the worst types to be quad weak too due to the overabundance of U-turn in the meta. U-turn is actually far and away the most used move, beating out 2nd place (Earthquake) and 3rd place (Knock Off) by double digit percentages. Part of the reason Celebi isn't viable is because it eats massive shit from U-turn.
Bug types DO deserve a buff however. Bug should be the best type in the game.