TikTok most definitely filled the void left by Vine. Vine was short video, usually chopped up, lots of one person skits. That type of content was not popping up on Instagram or Snapchat. Snapchat video would disappear, Instagram video felt more like a typical Instagram post but with video, or just throw away stories.
TikTok came in with short videos, collaboration tools, audio sharing, and has a realness that Instagram does not.
Also funny enough many Viners lived together in the same building so they could collaborate. We saw the same thing happen with TikTok.