>>57786971I'd say gen 5 probably has a higher ratio of good designs compared to what came after it.
It just has a lotta designs, so it has more stinkers numerically, but as far as ratio of good/bad design, it's better than the likes of Gen 8 to be sure, and if we're counting gimmick forms like megas into this ratio, easily above Gen 6, whose gimmick designs are almost universally garbage with I'd say less than 10% success rate of looking good.
Though, there is something to be said about Gen 1-5's inherent advantage of not using 3D models. It's harder to look at newer gens designs when your first impression is the lackluster 3D models. Gen 6 and 7 especially has it rough using the terrible 3DS rendering on the models, so maybe something like Dragalge or Shiinotic would be remembered a bit more fondly if we were introduced to them via sprites instead of the weird pixilated model mess that was the 3DS games.
I think it's 3rd place for best design ratio, behind the likes of Gen 1 and Gen 3. Maybe Gen 7 is above it, but again, first impressions did it no favors there.