Rating the Difficulty for Average Hikers
The internet is full of conflicting advice. Some say it's a walk; others say it's brutal. Here is a realistic difficulty rating for the standard Everest trekking route.
It is a walk. You do not need ropes, crampons, or climbing skills. If you can walk on a rough path, you can do this. It is physically accessible to most fit people.
You walk for 12 days, 5-7 hours a day. This cumulative fatigue adds up. You need the stamina to keep going day after day. This is the core challenge of the Everest expedition approach.
This is the X-factor. Altitude doesn't care how fit you are. It makes breathing hard and sleeping difficult. Managing altitude is what makes EBC a 'hard' trek.
It is tough but doable. With training and the right pace, ordinary people achieve this extraordinary goal every day.