Yes, the Japanese TPC does indeed playtest cards. They in fact have 19 full-time employees with varied skill in the Pokémon TCG that playtest new Pokémon TCG cards.
Here is the source for that: Gamespot “How New Pokémon Cards Get Made” - February 27th, 2020 (first shared here by @ptccards ). I will quote the relevant third part about the playtesting:
Step Three: Full-Time Playtesting
At Creatures, there’s a special room dedicated to testing the card game. It’s in the back of the small office, and it’s filled only with tables, chairs, and drawers upon drawers filled with years of Pokemon cards. Seven hours a day, five days a week, 19 playtesters play the TCG to see how new cards fare. (The odd number doesn’t seem to be a problem, apparently.)Because they’re mostly testing cards that haven’t been released yet, the playtesters have to work with what they have. Work-in-progress cards are actually stickers put on old cards so they can still be played in normal decks; if the illustrations aren’t finalized, these stickers will use generic art of the Pokemon (or whatever the card subject is) with the complete moves, name of the card, and suggested effects, HP, and damage.
The playtesters vary in skill to ensure the game is balanced for all levels of players, though all of them are expected to like Pokemon. Most don’t take notes, but they do submit reports and have meetings about the cards. Usually, feedback results in very mild tweaks to cards–slightly lower attack damage or bumping up HP by 10 or so. But in the case when a card is broken, the testers will bring that card to the game design team, who will decide how to proceed from there.
According to test room lead Satoru Inoue, those smaller adjustments happen “extremely often,” while they’ll usually see at most two or three drastic revisions before cards are finalized. Nagashima noted that competitive players will sometimes use released cards in completely unexpected ways, in which case the card has to be banned–he specifically called out Lysandre’s Our honorable president Card, which was banned in 2015 for making games severely imbalanced.
Even with all the playtesting, competitive players regularly surprise the team. Nagashima cited Shintaro Ito’s Mega Audino deck, which won him the 2016 Pokemon World Championships in the Masters Division, as a recent example–he didn’t expect the card to be nearly as viable as it was.
Nagashima’s favorite strategy, though, is one he himself was heavily involved in designing: the infamous Night March deck, which dominated much of the competitive scene in 2016 and won the US Nationals that year.
“I was only making it with the assumption that it would maybe make it to the finals, but not take the entire thing!”
Walking back through the office at the end of the tour, nearly every desk is filled with Pokemon toys and merch. It’s very clear: From the design and art to the test room, the most important thing for Creatures’ TCG team is loving Pokemon.
Apart from this article, I don’t know anything about playtesting in Pokémon, especially not during the WotC era.
The entire article is worth a read for anyone who hasn’t yet, since they also talk about designing and illustrating a new Pokémon. So not just the part above. And while looking for this article I remembered, I also came across another article I read before about the design of Pikachu, in case anyone is interested in that history/interview.
Greetz,
Quuador