Least satisfying Pokémon to use?

I had a couple Pokémon that turned into disappointments in my playthrough of Sun. The first was Decidueye, which went from my strongest Pokémon as a Dartrix to barely being able to take a hit and fainting almost every time I tried to use it. There was also Golisopod, which I specifically added to my team because I thought it was awesome only to find out that its ability made it almost useless. And Salandit, which I chose to make my main fire-type, expecting it to evolve into Salazzle. I didn't check the evolutionary requirements of any Pokémon because I didn't want to have anything spoiled for me, but I started to get concerned when I had my Salandit in the 30s or 40s (I don't remember what level I got him up to now), so I finally looked it up to find out that only the females can evolve but mine was male. That might have been the biggest let down of all, ruining my interest in both Salandit and Salazzle.