T58 should be 9.0BR. As I understand it the HESH that the T58 was to use IRL was insanely powerful.
I think this is both a balancing and a compression issue. The T58 has been a cash cow at its current strength and BR rating for the company, so this is unlikely to change until a sales dip sadly.
Edit: at least it’s not 8.3BR anymore? shrugs