You are right, this is a good place for getting/giving feedback...i see this trend on facebook or youtube people giving feedback to beats and there is like "make a 5$ donation to skip the line" is this shit real? People literally paid money so this guy can check their beats for like 20 seconds...
Frankly speaking, it doesn't surprise me at all. Similar situation is with labels and youtube channels that "release" music. I've been looking for some information about trap record labels that would accept demos and some of them have like 200 followers on Soundcloud or something like this and they want to charge you 10$ for guaranteed listen. But it doesn't guarantee you that they will accept your track. XDDD
My favourite situation took place yesterday. I emailed a guy that supposedly had "a record label" and I sent him my two recent tracks. He replied that he really liked my stuff and that I could find the prices of his services below. At first guy offered me a boost of my track either on soundcloud or YouTube for 50$. That was supposed to give me 1 M plays. I responded I was not interested as these numbers look fake and I didn't want to look that way. I asked him whether they could repost my track and whether there is also a price for this and they replied 50$ hahahaha. And when I checked their account on Soundcloud tracks that they reposted were played about 400 times so no, I'm not going to pay for a repost that would give me 400 plays. If you want I can send you screenshots from this conversation.
However, when it comes to feedback, imagine if you are a producer that has skills, is known, earns money on music etc. and someone asks you to provide them with feedback. Let's say you ask Anno Domini Nation or KSHMR for feedback. These guys could spend time they spent on reviewing your beat on doing something else or making a new hit song. For me such "reviews" or let's call it "musical coaching" are something similar to consultations with a personal trainer I would say. I perceive it in this way. You know everyone of us has been acquiring knowledge and improving their craft and that cost us time. Often a lot of time, hundreds, thousands of hours. Know-how is expensive so if you look at it in this way it is not that controversial in my opinion. But it's funny if similar thing is done by guy who has a little experience and/or their brand is not known to the public. He's just another guy that makes music. Then it's quite funny and I don't understand people who pay for such things. On the other side if there is a demand for such services and he provides supply then why not? My attitude towards it is quite indifferent and I would even say positive because you know they offer some services and they earn money on them. Whether it's worth it or not it's a different story.
So this is my humble opinion about it.