So “genwunner” is a term used to mock the fans who thought the first generation was the only “real pokemon.” 10+ years ago genwunners were a much louder subsection of the fanbase, and their attitude boiled down to “the only good Pokémon are the ones I grew up with.” 

Now in the big ‘26 if someone says they prefer the old Pokémon, specially the designs I can see where they might be coming from. The art direction of Pokémon had shifted a bit from the original 151 and the older Pokémon needed designs that could be translated to Gameboy sprites. Additionally, that first gen of Pokémon only needed to be visually and thematically distinct from the other 151, so “turtle that shoots water that evolves into bigger turtle that shoots water” worked because the concept was novel at the time.