RE: Commenting - waste of time
I will add to what @wakeupkitty said my personal opinion..
Regarding "people prefer a summarized version of what you want to say":
I sort of agree, as people feel safer staying with their own opinion. It is their comfort zone. Writing a long comment have a bigger chance in showing differences with your supporting evidence. On top of that, people would have an easier task of disagreeing with you, if you put no proof. So, it is much safer to read short responses. In addition, we can clearly see the change of behavior when the Social Media was introduced. People are now used to 20 seconds video summarizing all books of a certain author.
Regarding the fact that, getting a higher chance of response. It depends. I will not consider those who don't open their comments for the sake of this argument. For those of us who do, I think it is safe to say that putting a personal touch with sincere words would more likely be responded to it. Whether the comment was good or bad. For instance, if you comment with "Well said" doesn't sound like picking one thing that you like adding to, or asking for more clarification on.
For sure a personal touch will make the difference if read and if time. To be honest I find it hard to believe to see within 20 seconds all books of the writer. I doubt it's interesting for someone who loves to read (I still visit a bookshop and like to see myself before I buy and with us a good bookshop has places to sit and read and you can take your time.)
The answer to the question most likely is a mix between "no comment" and do what feels good for you since it's not said you will be read.
@el-nailul @eveetim