^ Unfortunately the above statement is incorrect. It's a common myth though.
All U.S. residents (don't have to be citizens/LPR) that is those who meet the IRS substantial presence test are required to file US taxes on worldwide income. What the OP is planning to do in respect to his/her taxes is correct.
OP, I won't worry about the 4506-T too much. You probably got hit with it due to your short credit history. Actually the more imp thing to do is that if you have been in the US for only part of the year, is to seek advise of a high end tax accountant & see if you could file non-resident taxes & not get taxed on your global income. If your global income is significant, saving tax on that would be more important than creating tax/credit history in the U.S. But that's just my 2 cents!
And if your priority is just to build that credit history, then no, Amex will not take other proof of income for your foreign sourced income other than that 4506-T so it's 100% better not to poke the bear.
I think if you had applied for that plat with 1+ yr history & higher limits, you would not have been hit with the 4506-T. Think the reason you got it - cause it's algos red flagged you - You have way too low credit limits for your 100k income & credit history for your age, so it doubts your income and wants you to prove it.