ORIGINAL: RVator
You should be able to do the 4 servo wing on a US. I am flying my US60 with a 6XAS and it will do crow. I have the ailerons on channel 1 & 6 and the flaps on a Y on the gear channel 5. I use a mix to add some down elevator with the flaps and the airbrake mix pops the ailerons up and adds a little more down elevator. To deploy crow I have to flip the gear switch to drop the flpas and flip the airbrake switch. The only thing I can't do is mix the flaps to the ailerons to create full span ailerons because of only 6 channels. I might be wrong but it seems I only need one more channel to do it. I do plan to buy a 9C for this and other models.
You are absolutely right, however as you noted, you are not flying it as a 4 servo wing, you are flying it as a 3 servo wing. With the flaps on the same channel, they can not follow the ailerons to crate full wing ailerons. THAT is what we mean by a full 4 servo wing. When the two flap servos can be independently set, trimmed and can work together or separately.
You have achieved crow but it takes two steps to do it. When we talk about a radio doing crow, it is as a single mix, usually on a switch, slider or the throttle stick.