Unless I missed something, no one claimed it's not legal.
There are lots of things that are legal but nonetheless not nice.
Just because it's legal doesn't mean you can't say "that's not nice" or "you shouldn't be doing that".
"It's legal" is not an argument here. It's completely besides the point.
That his own product ALSO gates access to, unless you pay the top tier for?
I don't think it's fair to criticize the competition for that, and not acknowledge that you do the same, no.
To use your own logic, if the founder of a FOSS project leader wants to have a conflict of interest (which is a negatively biased framing of them earning a living off their two decades of hard work), they’re allowed to. If they want to criticize someone else making money off that project, they’re allowed to. It is downright bizarre that you think it is acceptable that “Satan” can profit off Wordpress but with the creator of Wordpress you suddenly take issue with a “conflict of interest”.
To further use your own logic: Is Matt violating the GPLv2? No. OK, then why are you whining about him? He has the same freedoms that you ascribe to WP Engine or others. It just looks like you’re carrying water for an evil private equity firm with a long track record of being evil. All to attack someone who actually created a massive positive impact on the world. Yea no thanks - no one is convinced by this weird demand that Matt needs to step down.
You may not care about the history of your website, many people do.
The main issue at play is that Matt used the blog of a GPLv2 project to attack a competitor of his own for-profit venture for playing by the rules — disabling revision posts is an official and documented WP feature. The point is: if Satan themselves decides to use and make a profit off based on WordPress, he is allowed as long as they follow GPLv2, which is the case with WP Engine. (Satan as an alternative example for a PE equity is not by coincidence, btw.)
This is unacceptable behavior for a FOSS project leader, not to mention his explicit conflict of interest by running a for-profit company rival to the one he tossed under the bus exploiting his power and position in the community.
If you can't see what's wrong here, I'm sorry, I can't make this clearer.