You have no right to dictate what the goal of FOSS is about. It's also patronizing to claim Ghost made some kind of mistake here. They obviously picked MIT for a reason, which means they are fine with companies making profits from their unpaid work.
It's written in a very passive aggressive way. He's not congratulating substack, he's calling them out.
The attribution aspect of it seems intentionally misleading in my view. Are the MSM, who'll be chomping at the bit to attack their competitor, Substack, going to delve into the finer points of software licenses or rather just quote the tweet?
I'm not saying that Ghost should use the AGPL, I'm saying that this is a warning to other projects that use the MIT license and wouldn't want to see their work commercialized this way.
Otherwise, corporations can and will make immense profits from your unpaid work without contributing anything in return.
The goal of FOSS should be to create a new ecosystem that puts users in control, not to provide free labor to private enterprises.