Here's the old thread you were looking for.
Fennekin was actually winning by a huge mile back then, but it was definitely upon reveal of the middle stages that most of the Chespin fans decided to switch to Froakie because they were pissed off by Quilladin, but loved Frogadier being cooler. Braixen didn't really change Fennekin that much, but it was when the final stages came that Fennekin really started declining and Froakie reigned supreme.
Also, the 7th Gen starters seem to be ranking in the same popularity order as Unova's starters when they were first revealed - Snivy was initially most popular (thanks to the Smugleaf meme), Tepig was second most popular while Oshawott was least popular. It was once the evolutions were revealed that Tepig immediately became least popular, and it was all to blame on the Fire/Fighting repeat, whereas Oshawott got the cooler evolutions and gained its fanbase a lot. In fact, Oshawott literally went the same direction Froakie did, going from least popular to most popular.