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In response to the OP's picture, that's because there's just a lot of Pokemon introduced there. And unlike Gen 1 which they were throwing shit at the wall to see what stuck, in Gen 5 they had a better grasp on what a good Pokemon design is. Unfortunately in both cases, because of the large number of Pokemon a lot of them are also duds. Gen 5's are arguably worse for the reasons listed above, there's a lot lower lows compared to Gen 1 where the weird shit is either forgivable for being experimental or are amusing in their own right. The fucking Gen 5 monkeys have no reason to exist the way they do. Compare that to Gen 6 or 7 where there's so few Pokemon that it's harder for a bad design to get through and you see the difference a lot more. And then you look at Gen 8 and 9 and the huge design shift in those games for some reason, it's hardly comparable in some ways. If I had to pick between size and consistency Gen 3 might be a strong contender, but there's still a lot of weird Pokemon that are really up to taste at that point. Gen 4 is just kind of a mess and Gen 2's development seems to have cut all the edges off some interesting design ideas, of the two I definitely prefer the latter though.
