Since Cynthia is a functional reprint of Professor Oak's New Theory, one of the most powerful draw Supporters from the HGSS era, I don't think there was any doubt from the moment it was revealed that it was going to be a great card. The fact that practically every deck since UPR became legal has included at least one copy only solidifies that popularity.Cynthia I guess was a tad bit underrated (I think?) initially if the card went from 2 to 3 dollars to currently 4 or 5. I'll give her a mention since she's going to be the best draw supporter post-rotation and she'll probably jump up in price a little more drastically.
Even though it won Worlds 2017, I don't know whether to really consider M Audino a "good deck" as much as it was a really great meta call for that particular event. It was played by only a few Japanese players, won the event, and then died as soon as the rest of the world had it on their radars (since the majority of its good matchups rotated going into the next season). It was certainly an archetype that no one saw coming before Worlds, but Japan didn't storm the field like they did with Team Magma, so I don't think I would call M Audino a real game-changer. If anything, the whole thing still feels a bit like a fever dream more than anything else... hahaM Audino-EX was really good 2 years ago, but nowadays Night March is gone so it doesn't have any threat it could beat and it can't take a hit from either Buzzwole or any form of Necrozma so her playability is gone.