In addition to other commenter, your entire premise seems to ignore the fact why Goldman and City at large are so heavily pushing financial "passportization", if as you suggest UK finance industry can operate seamlessly without it.
Difference being that sure the UK can operate as it wishes, but EU does not have to bless that operation. EU regulations which govern EU corporations can dictate rules which are incompatable with UK model, that require the significant steps in financial chain to be under EU jurisdiction at relevant stages. Passportization was the "As long as we are UK-legal, nobody in EU can do anything about it". Losing that means that they can.
And sure, UK can go it's own way, it can function as offshore for Russian oligarchs and non-EU corporations, but without passportization, the EU is free to claw back sovereign control over financial sector interfacing with it's own economy, it can simply state that financial arrangements occuring outside it's regulatory framework will not be able to enforced re: actual EU assets.
This reflects on Ireland in that it will not have the "lowest common denominator" advantage, it will be fully within EU regulatory regime, same as FR, DE, etc. So the legal benefits of UK will not carry over, and it will simply not be as distinctly advantageous locale to operate under. More broadly, sentiment is growing across EU against tax avoidance enabled by Ireland, Netherlands, and Luxembourg. "Profit transfer" tax evasion is far from secure, especially given the impact this has on governments under budget pressure. This also is subject to EU regulatory regime legitimizing the necessary legal schemes.