Like Fizz stated in the comments, In-game teams may look better then they are in competitive. And like Fizz also stated, before Serperior got Contrary Serperior was in NU, that's almost the lowest tier already.
People might not like it because of it's pre-evolution already, growing from hands and feet to no feet and no hands.
And of course, being a starter that looks more feminine but it still has a 87.5% chance to be male.
In my opinion it is gorgeous, and superior (yes, my puns) but there are always people who dislike Pokémon for their own reasons.