Since I review cartoons I unfortunately have had to see a lot of reaction channels pop up in my recommendations which do nothing but put the shows I review into one corner of the screen and have their face in the other corner.
Yes it's bad, lazy, and constitutes theft since it doesn't fall under fair use. Most of the views come from people who are ignorant of better ways to watch shows through shady means.
And usually given enough time these channels are shut down (typically after they get huge). So at least there's that; I have the relief of knowing if you try to scam the system long enough, eventually your channel will be destroyed. I've seen YT put the hammer down on 3 channels so far (strangely these people get to keep having YT channels, which is annoying because YT is supposed to ban your entire ability to do that).
The horrid thing though is that for every reaction channel to die dozens crawl in to fill their place. Reaction channels are like ****ing cockroaches - I'm not gonna sugar coat that statement. And they know they can persist because they seem to never get any repercussions beyond losing their channel. I'm sure many of them are even happy to make a buttload of money from blatant theft and come out of it smelling like daisies.
Short answer: Yes reaction channels in the manner they exist today are bad. More involved commentaries can be OK, but they are far more rare.