TikTok is not primarily livestreaming, but it does have live streams (with live chat overlay on top of video, looking very similar to live streaming interface of Instagram or Periscope)
So apparently TikTok Live is mostly a competitor to those two (and maybe YouNow) but not to widescreen/desktop-oriented streams of Twitch
YouTube Live on the other hand is very much a competitor to Twitch (livestreaming to millions and NOT auto-expiring/deleting past broadcasts by default is something only YouTube can do for now)
So apparently TikTok Live is mostly a competitor to those two (and maybe YouNow) but not to widescreen/desktop-oriented streams of Twitch
YouTube Live on the other hand is very much a competitor to Twitch (livestreaming to millions and NOT auto-expiring/deleting past broadcasts by default is something only YouTube can do for now)