Facebook is ripping off a larger variety of apps than WeChat, it seems more like they're trying to push into Snapchat's market share.

I'm not familiar with payments being a feature on iMessage or Messenger, though. Unless you mean just the money transfers to friends, which existed on Facebook's desktop Messenger first IIRC, so it doesn't appear to be ripping off WeChat (which in my experience doesn't really support money transfers in quite the same way, unless we're talking about hongbao).

Also, weren't stickers a thing on Kakao Talk and LINE before WeChat?

Wechat supposedly ripped off a lot of features from LINE, but since LINE is a Japanese/Asian thing, most Americans know even less about that than WeChat.

line is from naver (korean company), but apparently no one in korea uses line... (100% kakao)

surprised to see Line everywhere else in asia though (seems initial popularity decides a lot for these messenger apps - or some extremely unique features that can't be copied)

Line was originally Japanese, it was just acquired by a Korean company, explaining the lack of market share in that country. I think Kakao predates pretty much all modern messengers, including Kik, so it's kind of surprising they never reached out of Korea very much.