Is gum flap surgery for a 5 mm pocket considered a minor type dental procedure when compared to other invasive surgical types?

Yes: Flap surgery is a relatively minor procedure compared to other surgeries. However is is still surgery and you should be prepared for some discomfort for a few days. Medications should control any pain you may have.

Somewhat. : It depends on how many pockets he is fixing at the time. Doing 1/2 to full mouth at a time is more major than simply 1 small area.

???: 5mm pocket can be cleared up with a scaling and home care. I would not suggest flap surgery at this point.