Ahem... Time to show my age here.

Some of the early radios back in the 60's were NOT proportional. You had toggle switches that would return to center when released. One switch per channel. But these were the first radios to give you 4 channels! (A big deal in those days!) It even had it's own name - "Full House". But you had to "blip" the switches to avoid getting full deflection of the control surfaces. (the Throttle switch returned to center, but the servo stayed where it was last set)

The next generation of radios featured "Full House Proportional" Those were some of the first "2-Stick" transmitters, and WOW!!!! That was the hottest thing ever!

Of course, nowadays you rarely hear the word "Proportional" unless it is used to say things like "Retract Servos are NOT Proportional"