Well, number one, I would be reticent to say any individual example is a clear case of fair dealing, because that would be a case-by-case instance. For example, it's theoretically possible that a react video may use a sizeable portion of the original content. As a consequence, it may not actually be an example of fair dealing.
However, you raise a fair point with respect to how we balance those individual rights. This is again why the appeals process is critically important. What happens is this: If it is appealed and if the rights holder decides they are not going to release this claim, then the individual user who got flagged incorrectly can then reject that, in which case the video is permitted and the rights holder would have to file a formal takedown notice to remove that video. At that point it goes to a counter-notice provision, because we therefore have a dispute between two rights holders that we actually have to let them sort out between themselves.