It does not surprise me but you seem not to understand how these things work. Act of Union was the worst thing that happened to the Irish people. It's what caused today's mess. And the inability of the British government to let go of Northern Ireland in 1922 (which again, is an aftermath of the Act of Unions)
No, I understand what went wrong and it was not the Act of Union.
A Dublin parliament ruling Ireland would have been ideal but for one tiny snag. Catholics generally didn't have the vote. So the Dublin parliament was largely unionist and not really concerned about the lives of ordinary Irish people. So it being scrapped wasn't that big a deal, it replaced misrule by the local Protestant elite with misrule from Britain.
And Northern Ireland had nothing to do with the Act of Union. It had to do with migration either through Plantations whereby the Ulster Catholics were supplemented or replaced by the more loyal Scots and Northern English or the unplanned kind of migration where people in South West Scotland found new homes in North East Ireland of their own accord.
A Dublin parliament that decided to sever the connection with mainland Britain would have also triggered the "Northern Ireland" event.