There is no promenade deck as such, i.e. one that goes right round the ship. There is access out onto the side deck from the several places on the main decks (where the restaurants and bars etc are located). I don't think you will have any problem. We (although not disabled) found the staff extremely helpful if you just ASK. Most of the criticism seems to be from people who wanted things but expected the staff to be mind readers. I witnessed staff helping people in and out of lifts and accompanying them to show where the gangway was located etc etc.
Not true , this ship although staff friendly ,is exhausting for wheelchair user so big and ages to wait for a lift .dont expect wheelchair tenders although a new ship.