I can't comment on the availability of power sockets, but you shouldn't feel restricted by not being at the window, although if they located the sockets between seats that would be better. The main issue is whether or not they are working.
I think it is unusual to get the person by the windows to cooperate with having a wire over or behind their legs and that is if they aren't using the socket themselves.
The 59-reg Panthers don't have sockets. The more recent Interdecks and Double deck coaches do. Can the USB socket be used independently of the 3-pin socket? I've never crouched down to have a look at the fitting in detail and, as noted, it doesn't always work.
Speaking of other things not working, why are coach drivers so reluctant to have the air vents switched on? If you got on a plane and found no forced air on, you wouldn't be best pleased but coach drivers almost never have the vents on. Given passengers have control over their individual vent, it should be up to passengers, not the driver.