First, I’m sorry for your loss. I’ve lost too many friends and family over the years to various things and each one hurts.
As for the death certificate, the question for the hospital is not “would he have lived another 10 years”, but rather, “would he have still been alive at the time of death were it not for the disease.” From the CDC’s guidance on death certificates, they need to list the underlying cause of death, which is “the disease or injury which initiated the train of morbid events leading directly to death.” The smoking and COPD would almost certainly be listed on the death certificate for context, but if he would have lived a month or a year longer were it not for COVID-19, then COVID-19 is the Underlying Cause of Death (UCOD).
Why? Because we’re all going to die some day of something, but the death certificate notes what actually got us.