Personally I find this to be a problem with all HTC phones. I had two M7's. The first was ridiculous, the second was toned down a little I suspect a different motor.
Anyway I guess you can change it with root/kernal settings.
Sent from my HTC One using xda app-developers app
yeah, had the same issue with my m7. Fixed that one with custom kernel.
However, that modified the vibration globally, including touch vibration and that ended up being barely felt.
EDIT:
also, can you please point where exactly would I find the file that deals with vibration in root?