How come today's waifu are nothing compared to her?
Because most of them are generic cutout stereotypes for harem anime.
Because that's what happens when industry recognizes a formula that brings in money. The Urusai Yatsura anime/movies today would probibly be made by some shit studio like Trigger or kyoani and they would be nothing like the show we know and still love today.
Romiko likes to give her characters lots of flaws to make them interesting and in most cases it works out nicely.