How much of a difference does it make in practice? Just the platform does not seem like that much more information.

Further, I'd wonder if, while the actual OS is fingerprintable (as the various discussions seem to suggest), reporting one OS whilst actually being on another flags the user as interesting/has something to hide (i.e. they are probably using Tor Browser, not just Firefox).

There's also usability to consider - if this results in more people using Tor Browser, or not disabling things to try and work around it, that might be a net gain.