If you have been removed as an Authorized User (AU) then Amex reports the "removal" to the bureaus. I was an AU on my wife's AmEx and Chase. I just checked my Experian File. The AmEx is still on my report in the Closed Account section and is marked terminated. The Chase card I was an AU on is TOTALLY DELETED from my Experian Report.
You mentioned Debt to Income (DTI). DTI only factors into OPEN accounts. If you have been removed then the Debt (balance) they have is not attached to you. Suggest you contact AmEx directly and ask them. Quickest way to find out is to sign up for a free account at Experian. It will show you Open and Closed Accounts. If the AmEx is in the Open Account section then it IS factored in your DTI. If it's in the Closed Account section then DTI is NOT factored in. Let me know how it turned out [PII Removed]