Part of the attraction of BA's upper deck, for me at least, is the additional space which window seats have between seat and sidewall (containing handy storage bins, some of which, but not all, are quite cavernous) plus not having large numbers of passengers streaming past you to reach their seats if you choose to board early.
Much as I like the current version of BA Club World, for me the smaller upper deck of its 747-136s with non-flat bed Club seating was almost as appealing. I preferred it to the main deck when configured with 6-across economy seating.