so i have a few thoughts on "that's not how boundaries work" and "you can't just tell fans they're not allowed to ship anymore".
i am aware, and i do agree, that boundaries generally shouldn't look like "you're not allowed to do this". they should look like "if you keep doing this, i will [remove myself from the situation / other consequence you will draw.]"
but sadly, when it comes to creators setting boundaries with their fans, it isn't that easy. because removing themself from the situation, for a creator, would in this case mean stopping content creation.
and while "what about just having blocked tags" is a good argument in theory - i'm 99% sure that in his explanation, Pyro said it wasn't just seeing the shipping content that was the issue, but also simply knowing it exists and that a significant part of the fandom is engaging in it.
like... both Pyro and Maddy have said that they're well aware of how much they're taking away from people, and that they didn't take this decision lightly at all. Maddy quite literally had to do this for her mental health (pleaseee go read her post if you haven't).
now, do i personally understand why someone would be a nervous wreck (as Maddy has phrased it herself) just because they're aware people are creating shipping content of their or their partner's characters? can i relate to it? no. but i do believe there are factors here, like personal sensitivities and character bleed in rp, that i couldn't possibly relate to, but that are in fact significant. and, more importantly: i think that anyone's feelings - and mental health!! - should be respected and taken seriously regardless of whether they're "reasonable".
so, again: sure, phrasing a boundary as "you can't do this anymore" seems harsh, maybe even wrong. but it is simply a rephrasing of "if the fandom keeps creating this shipping content, then Maddy will have to remove herself from content creation (or at least from rp and all related spaces)".
and if at the end of the day, you care so much about your yaoi that you don't care about the personal and professional consequences this will have for a content creator, then... have fun with that, i guess.