Always good to have different opinions.
I guess part of the reason why I don't like it is because Gen 1 is my favourite and many gen 5 Pokemon were copy's but different and worse for me. Bouffalant/Tauros, Throh/Sawk - Hitmonchan/Lee Patrat/Rattata and the Simi's being cheap rip-off Eeveelutions (teaching you how to use the stones). It had it's gems though, I'll give you that. The story was also very good.
Yeah I can see where you're coming from. Most of the "equivalents" if you call them such I actually like equal to (and in a few cases, moreso) than their old counterparts. (Gigalith is fantastic, for instance). Bouffalant is really charming to me design-wise. I also happen to love both the Hitmons and Throh/Sawk for differing reasons. You could argue though that the Patrat line is just the obligatory rodent, as every generation has had that kind of Pokemon. I actually did never see the Simis as Eeveelution counterparts, just as their own weird little trio. (Admittedly they're not my favorites in the generation, though).
And honestly? Your argument is definitely valid. I view them as their own charming creatures though and like them as their own kind of thing, though. I do think that even though there ARE some weak links, I think most of the Pokemon in the generation are absolutely fantastic. (Two of my four favorite Pokemon are Darmanitan and Lilligant). The Pokemon, the locations, the story (still the best story in the series, Sun and Moon just doesn't cut it in comparison), it all just kind of combines into what I consider some of the best Pokemon all came out with. (I think that Platinum is the closest we've gotten to a "perfect" pokemon game, but BW are still close behind as my personal favorites).