I think the issue of these pyro specific cosmetics breaking team recognition comes up a lot, and for good reason, but in a situation like competitive play the pyro doing this is really failing to achieve two things:
- Competitive players are extremely quick on their feet and can usually recognize that the pyro staying with them and spy-checking / NOT attacking them is likely their teammate or enemy within the first view of the player, and deal with it accordingly
- Running these cosmetics, if anything, has a chance to mess up the pyros own team just as much as the other. As rare as it would be, teams allowing this would honestly just be stupid on their own right. Would obviously only possibly affect extremely low divs.
So I think allowing it is just saying "If you're doing this, it's really stupid and only has a chance to harm your own team more than anything.