I would make the point you dont weight train for cycling performance (the benefits are probably pretty small), you weight train for health and general conditioning for lifes activities. All (well most!) of us have lives outside of training, moving a TV, yardwork, putting boxes up in a storage area. Weight training should help give you the functional strength to perform these activities without hurting yourself. It also has benefit in maintenance of bone density and avoiding muscle mass loss with aging.
I would add that the closer the weightlifting activity to the movement the better the carryover so I cant see wall sits being a lot of help to a triathlete/cyclist. But if you were a triathlete/cyclist who liked to go skiing over the winter some leg strengthening including wall sits as well as balance and plyometrics could prove beneficial.