Yes but the UK can't unilaterally nope out of reporting requirements because the EU can simply refuse to continue with the previous passporting abilities afford

Yes but the UK can't unilaterally nope out of reporting requirements because the EU can simply refuse to continue with the previous passporting abilities afforded to UK finance. If the UK wants to continue with London being the gateway to the EU financial sector, they'll need to adhere to the EU rules. With Brexit, the UK has now no say in what those rules are beyond some saber-rattling. I mean, the UK can certainly just offer a very loose regulatory environment, but that's useless on it's own if other jurisdictions refuse to cooperate. The extreme measure would be to put the UK on the uncooperative tax regimes list, which would mean that nobody in other countries would touch business established here.