No one's talking about your personal project here. The audience is teams of people building software to be used in production.
You can even justify using malbolge for your hobby project with "I like it" or "It's just for fun".
If your company is only going to pay you for producing malbolge code, then you write malbolge or quit. If you decide to stay, then trying to change their mind might be a good idea if you can spare the effort.
They should hold, but the RESF can be too absolutist. The wording of the tweet encouraged that, so I was just trying to push back on it.