For example, do we agree that voting on comments is good? If that is the case, then the number of different people who can be voted on is rather limited since the majority of people do not place appropriate comments. Is this considered circle jerking?

NO, not at all.
And upvoting comments sure is very good.

Unfortunately, we do see a totally different "curations" from some of these TOP20 leaders, which has nothing at all common with comment voting, or alike.
Like this:

A ~50K Leo stake holder (which consist of 99% stake delegated, and 1% his own), during whole week spends ~7 minutes for his curation job, upvotes a selected 24 (twenty four) authors, every day the same and the same, all with 100% voting power.
76 votes during 7 days, but NOT even one single vote on a comment, not a single vote with less than 100% power.

I would be not surprised, if data retracted for a longer period (not seven days, but for month or two), would still show his voting power 99+% spent on the same selected 24-25 authors. I have noticed this behavior before, and maybe it is time to pinpoint it to others.
Before this type of "curation" gets more followers.

It would be also quite interesting to dig a bit deeper, and see from where exactly his 99% delegated Leo power is coming.
As you all know, everything is on the blockchain, forever, all what is needed is just have some time and start digging.