You state that, "The IAEA confirmed compliance with the narrow technical rules of the JCPOA" To state the obvious, that was the IAEA's mandate: No more, no less. Why expect either the IAEA and/or Iran to go over and beyond the terms of the Agreement? The JCPOA had the support of the UN PS plus Germany and the EU, and had the effect of halting Iran's progress towards attaining nuclear weapons. I'd call that success and far from flawed. Moreover, although the Agreement was time-stamped, there was nothing to prevent negotiations continuing - or strengthening - the Agreement. Nothing that is until Trump's withdrawal of the US. The idea that Iran would effectively leave itself at the mercy of Israel and Saudi Arabia by agreeing to voluntarily giving up any military deterrent (it's missile systems, etc) as you suggest was - and is - a complete non-starter. No other nation would be expected to agree to such terms so why expect Iran to do so? Although sanctions make things more financially difficult for Iran, it still continues to fund Hezbollah. The presence or absence of a JCPOA type deal does not prevent it. Indeed, how exactly could Iran be preventing from sending funds to Lebanon and Palestine unless their budget was managed by, and, from a third party (presumably the US). In reality, we had a deal. While it couldn't be claimed to have been perfect or to have permanently solved any major problems, it did at least prevent existing problems from getting worse which was a lot better than the situation since 2018. The irresponsible behaviour of Trump by withdrawing from the Agreement and his behaviour now - without seemingly having any idea of what the final outcome either should look like or is likely to be - is unfortunately proof of that.
