Hm, I thought it was missing some big stuff -- I had some impression that BBBA was targeting a 50% reduction in emissions by 2030, and the IRA reduced it to 40% (this was the only actual list I could find in quick searching, and says it was missing "A range of policies that were previously part of the Build Back Better Act ... like electric power transmission, CO2 pipelines, and building energy efficiency" which makes basically 0 sense to me and sounds like an LLM hallucination. What the fuck is a CO2 pipeline.)
I wasn't able to find a really detailed breakdown of what might have been missing from it, so honestly I could be wrong.
I do agree with you that the IRA was a massive step forward from the usual US government "total inaction or else make it worse" policy, and that Manchin supporting it despite the fact that it was actually trying to do some significant good things is a shocking and welcome surprise. You kinda have a point there.