I too am a diabetic, type 2, since 2010, and I'm on a low dosage of Lisonipril to aid in keeping BP will within the desired range. But none of my PCP's have expressed concerns with cardiac issues beyond "You're in the green arc, stay there and don't get out of it".
I don't think your "because diabetics can develop heart disease more easily" is the full reason. While that statement is true, something else may have been reported to them from your PCP or AME to cause them to think the stress test is warranted. You might check what the AME sent up to for any clues.
I was "newly" diabetic when I did my first medical certificate application, and have renewed 2 years ago, and am due for renewal next month. Never have I gotten a letter from the FAA asking for the stress test. To my knowledge, being diabetic with no related complications isn't enough to trip the need for the stress test.
Besides diabetes, any other obvious cardiac related issues that are not yet in evidence?
For the benefit of anyone reading the thread, good management of diabetes through smart food choices, increasing exercise levels, and dropping weight goes a long way toward quality of life and keeping the FAA AMCD happy.
Since mid summer, I made a choice to walk 5 days a week instead of 2 or 3, and go 3-4 miles instead of 1.5 to 2, and kept my total carb intake per meal to 35 grams or less. Results have been very positive with a 13 lb weight reduction, average fasting and pre-meal finger stick numbers down to 108-115 from 145-160, and BP reading at the doc's office well within the green arc.