As to both of your experiences, it's a shame neither of you experienced the real reason many of us make a point to stay at the CH; a room facing Parliament, Big Ben, and the Thames. It's a shame neither or you got the chance to enjoy a room with this view, truly one of the finest views in the world from a hotel room. To play the devil's advocate, it's true that the CC has superior service and first class (if not world-class) rooms, but lots of hotels have this, in and out of London. But few hotels anywhere have rooms with an equivalent view to CH. If you secure a view room with a balcony, having breakfast or sipping wine on your balcony while enjoying the view is unforgettable.
That being said, I did not experience many of the problems at the CH as reported in this thread. My room was fine, but maybe not quite as fine as the CC. The front desk personnel were helpful at CH, but not quite as service oriented or defferential as the staff at the CC. On the other hand, the promenade along the Thames by the CH and its location among top attractions more than makes up for this, in my opinion. To me, the choice between CH and CC becomes clear, once one decides what one is looking for in a London hotel. Top service and rooms, with a good location, choose one. World class views with a great location, and rooms and service that are adequate, choose the other. But all bets are off if the CH room is not with the view.
As to Marriott hotel categories, as I understand it, these categories are strictly for the purpose of assigning a point value for awards at the property, and are determined by demand for awards at the property.