No, with the switch dedicated to a channel, the switch won't be dimmer. It would just behave like the switches on non-Emerald sabers: full brightness when the saber is on, off when the saber is off.
It only dims when you put the switch LED in line with a channel...for example you chose Ch 4 to be in line with the switch and set the value of Ch 4 to let's say 50. Then the switch will be drastically dimmer than an AV switch that is dedicated to Ch 4 or always on. But you still have all 4 channels available for mixing while the dedicated option connects the channel 4 to the switch only so that you loose it on the main LED and, like you said, end up with an actual 3-channel driver. The switch LED's brightness is still at 100% when dedicated to a channel.
I've just tried adjusting the 4th channel that is dedicated to the AV switch and lowering the value definitely makes the switch illumination dimmer all the way down to 0 where the switch does not light up. Altering this channel does not effect the blade colour in any way.
