I think once we see the price of steem recover then comments will start to get more votes once again. It can be hard to give a 100% upvote on a comment if you want your own account to grow, so like you said, people are more likely to visit your blog page and vote some of your content when you have left a nice comment, that way you and them get a reward whereas a vote on a comment no one may get a reward unless you have a shit ton of SP.
So I am not so sure that HF21/20 killed the engagement aspect, just that the ability to give a vote of any value to a comment is a tad bit on the high side right now.
You might be right and I hope so. I have always liked to reward my audience something, so it would be awesome to upvote comments again.
For the smaller accounts SP wise (Under about 2300 SP) it is very hard to justify a vote at 100 % just to give a 2 cent reward, a full power vote is better spent on a person who commented on a post is to vote on one of their post.