Think about it. The idea here is that the anthrax conspirators were a completely separate group to the 9/11 conspirators, but that they wanted their work to be perceived as of a piece with 9/11. In other words, after a shadowy terrorist group had just killed thousands of people very publicly and gruesomely, the anthrax conspirators immediately set out to create the impression that the same group also had access to a weapon of mass destruction. It's an action which seems more likely to flat out deter war against the terrorists, than to channel the war in a particular direction, which is the intent usually ascribed by the 'insider' theories.
How do the anthrax letters frame Iraq anyway? They don't mention Iraq, they don't allude to Iraq.
Just three years before, the USA had intensively bombed Iraqi WMD facilities, and had adopted an official policy of regime change in Iraq, out of fear that weapons like anthrax might be passed to terrorists. The Secretary of Defense went on TV and specifically said that a small bag of anthrax could kill half of Washington DC. The Iraqi biological weapons program was the greatest source of concern for UNSCOM. Iraq admitted that it had managed to weaponize anthrax, albeit in liquid form.
So it's the mere presence of weaponized anthrax in the letters which was guaranteed to make people think of Iraq. As you say, the text in the letters ("DEATH TO AMERICA") is more reminiscent of Iranian sloganeering.
The question of Iran, Iraq, and al Qaeda sponsorship reminds me of one of those logic puzzles, where you have (say) two giants at a fork in the road, one of whom always lies and one of whom always tells the truth, and you have to figure out which road leads to your destination by asking just one question.
In real life, both giants mislead to the best of their proficiency, so asking questions to find out which is the road to Country A, your destination, is useless.
Instead you say, "Did you hear that they're giving away free beer and WMD in Country A?" It doesn't matter what they answer, neither giant will take a chance on the other getting to Country A first. They'll both be headed in search of the free beer and WMD as soon as possible. Discreetly follow them.
So, anthrax makes people think of Iraq.
The phrasing sounds like Iran (or maybe Hezbollah or some group like that).
Genetic analysis of the DNA links the anthrax to USAMRIID.
By the same token, 9/11 points to Saudi Arabia, since most of the hijackers were Saudis.
And other evidence points to Pakistan and ISI (the money trail, the support for the Taliban, the marketing of nuclear technology by A. Q. Khan, and so forth).
In other words, there are plenty of little hints pointing in a wide variety of directions. Some of these may be spurious (just coincidences). Some may be disinformation (false flags and/or frame-ups). Some may be real.