I feel like the post paints with a really broad brush. The author is targeting one specific segment, while also linking to a wikipedia article with a much broader definition "A mastermind group is a peer-to-peer mentoring group used to help members solve their problems with input and advice from the other group members."
Microconf offers Masterminds, they're basically acting like a matchmaker. For your entry fee (determined by ARR) you get introduced to 5-7 other folks at a similar level. Your group then meets up on a regular cadence to discuss topics. My group has been meeting every other week for 6 months or so. I joined for our new project, so $250. We don't get speakers in, but we do get access to a great group of folks to bounce ideas off of, outsiders to offer opinions, and occasionally hold us accountable.
About half our drop has dropped off (and we've added someone new on our own), but I've gotten a fair amount out of participation.