Gen 5 has more Pokemon than any other gen, so there are more opportunities for bad Pokemon, and more opportunities for Pokemon like Chandelure and Golurk that are awesome. Every generation has its bad Pokemon, Voltorb, Corsola (I do love its Galarian form tho), Luvdisc, Lickilicky, Alomomola, Quilladin, Bruxish, Carkol, and freaking Scovillain. These bad Pokemon have Pokemon within the generation that more than make up for them, like Rowlet and Decidueye more than make up for the bad generation 7 Pokemon, this is even more true for gen 5, because there are so many opportunities for being bad and many more for greatness.
People keep complaining about Vanilluxe, Garbodor and Klinklang.
I look at the bright side.
We got awesome stuff like Druddigon, Golurk and Braviary.