I just tried seeing what using the non-simplified calculation does. I get the same end results, and Form 1116 looks identical; but the Form 1116 AMT has differences. With simplified, Part 1 is completely blank; with non-simplified it has column A filled out. With simplified, Part 3 line 15 is blank; with non-simplified, line 15 has a number in it (it gets populated by line 7 from Part 1, which now is non-blank), and subsequently a few other numbers are a little different.
If it had turned out identical, I'd probably go for it (it doesn't seem like TurboTax has prioritized this issue at all); but given the differences and the IRS warning, I'm a bit hesitant.
I'm also not sure I'd trust the "tax expert" (though maybe if it was in writing). That doesn't mean the IRS won't come back later and not like what you did. I talked to an Intuit "tax expert" the other day, and she made up a bunch of nonsense about how mine was actually being rejected because TurboTax files an amended return (1040X) after a rejection, and the IRS doesn't accept those until March 25. I'm pretty sure both of that is wrong.
