Hi @transisto, sorry for the late reply, but this post only now came to my attention. I know you didn't request a response but I'd like to make clear the facts as simply as possible.

1. I'm not now, nor have ever been a member of the Discord group mentioned.
2. I did formerly have an arrangement with @cryptopassion to support each other's content through the Steemfollower service. He approached me through Steemit chat about the idea.
3. I found the arrangement unsatisfactory, and called it off several weeks ago. This should be obvious by the fact that in your diagram, the arrow from @d-pend to @cryptopassion is larger in size than the reverse (indicating something other than a 1:1 interaction.)
4. I have never had any arrangement with the other users that you mentioned.

Why did I ever try such an arrangement?

As a relatively new user of Steemit (since June 2017) and believer in its potential as well as that of the STEEM blockchain, I have been heavily investing by buying SP, renting delegations, using bidding bots, etc since that time. I have basically tried every method I could find to help grow and develop my Steemit account. Some methods I have found unsatisfying (for example, I no longer use bidding bots, preferring to simply buy more STEEM with the SBD that I earn) but it has been a fascinating learning experience. At the end of the day, my main motivation in building on Steemit is the ease with which I can give support to the many amazing individuals adding value to the community.

Why I found vote-agreements unsatisfactory

As I mentioned, I have tried many things to help gain exposure for my content, including voting agreements. I found them quite unsatisfactory and no longer maintain any. The main reason is how nonmeaningful they are. They boil down to pure profit regardless of quality, as you stated in your post. I don't think this is the way Steemit is intended to operate, though I respect the right of any stakeholder to use their voting power in any way they see fit, including to produce pure profit. The best way to prevent the gaming of the system is to implement changes in the fundamentals of post/comment/curation rewards. I am willing to not operate based on pure profit because, philosophically, it is not fulfilling to me, but others may not agree.

Conclusion

The type of voting collusion you describe is extremely widespread on Steemit. Whether the agreement is explicit or implicit, it has to do with basic human psychology of tit-for-a-tat, and how Steemit is programmed to function. Both aspects encourage people to vote about the same amount for the people that vote for them. I find explicit agreements (unconditional, without regard to quality) very unsatisfying which is why I no longer maintain them. I tried them in the past in an attempt to get more exposure to my content and to help build my account so I can support more people like bigger whales can. Still, I am not against conditional arrangements (trading votes providing the quality is sufficient, though not for indefinite periods of time.)

Anyway, sorry for the monstrous reply! I respect the work that you do to keep rewards equitable in the Steemit ecosystem and hope I can do my part as well. I wanted to be fully transparent about my involvement here, as it has been my intention since day one joining the site to avoid drama and misunderstandings by being as honest and open as possible.

Thanks @transisto, let me know if you have any questions or comments. Have a great day!

@d-pend

Edit: self-upvoting to get top of the thread for historical reference.