With a champion that hasn't been newly released you have already seen how they play and have experienced their abilities and what not.
PBE testing is an advantage some players have but there are always discrepancies such as bugs. PBE matchmaking is also horrendous, if you aren't Gold+ then don't play Kindred right after release, even if you've practiced her in the PBE.
Some players actually believe that because the enemy doesn't know how to play against a Kindred that she would be the winning/carrying ticket even if they haven't every played her before. That's false. The majority of players (I am assuming) already know what she can do, the enemy of the Kindred is not bothered if the Kindred performs well or not, it is up to the Kindred player to execute the champion well not the enemies.