The option would be radiation treatments. Probably with concurrent chemo. While a 6 hour surgery doesn’t sound conservative, compared to 6-7 weeks of radiation it may be. There’s not a lot of detail in your post about the surgery and what structures and parts of the anatomy will be impacted. What long term functional or esthetic concerns it may cause.

Personally I would want to understand all that in detail, and the doctors are obligated to discuss that with you. You also do not say if his treatment plan was decided on and developed by a tumor board composed of doctors from different disciplines and training. If that is being determined by the ent only, who is only trained in surgery, this choice is obvious. A tumor board would have both a radiation doctor in its group, and a chemo doc to weigh in on options. The best plans are developed this way, not by a doctor trained in only one treatment modality. I would explore this to end up with the best idea developed and agreed to by a multidisciplinary group of doctors.