18awg is more hassle than it’s worth. I would only use 18awg for emitter wires over 4 inches and over 5 amps. I use 22awg for springs and emitters under 5 amps, 20awg for emitters over 5 amps.
I like the challenge to wrestle with 18awg, it is part of the fun 
i have even thought about buying some silicon 14awg just see if it is even possible to use 
But you are right he wanted an easy to install driver so 20awg or 22awg would be easier & only lose him a few % of output.
I am not so good at good enough 