Lower your expectations and be honest with yourself.
How important is an upgrade when you are traveling alone on business?
In my 45 years of frequent travel (even before there was a frequent stay program) I found the only 100% guaranteed upgrade to a genuine suite were at facilities where you were on first name basis with the GM.
In the current environment a Diamond upgrade is usually perfunctory and would require an advanced statistical test to determine the difference between the booked room and the "upgrade."