That's true if all you know how to do is turn screws. That's where some engineering comes in handy. Definitely not a 20-minute tuning procedure to fix that problem hence higher labor costs.
Even if you knew more than turning screws you cannot get rid of all distortion.
We mere humans to not posses that level of technology which will probably require exotic substances not known to man or violate the laws of nature to achieve.
It may be very low and inaudible but its there.
We are talking about CB radios that are built to a price based on antiquated designs.
I am surprised they are as good as they are, to be honest.
And, it's AM modulation!
I have not watched the video as yet, but what I can tell you without watching it is that there is some form of distortion in any radio at any time and it can be measured provided you have an instrument with sufficient resolution.
Ask Fine Tunes to measure it.
If he is honest as you say he is, he will do the test and show it.
That HP8924 he uses has the capability of doing such a test.
Now, I think we can all agree that the instrument (the 8924) even as old as it is and meant for use with legacy cellular networks can generate far superior signals to any CB radio out there. It's just better at it plain and simple. Better built and designed in every way to a CB radio. It's quite capable of measuring distortion in the audio.
It can't show 0% distortion. It's own resolution is +/-0.1%
Go look at the specifications right on the Keysight website right now.
Verify this for yourself.
This is why you get the responses you get.
You jump immediately to implausible or downright impossible and say he (Fine Tune) can do it.
The way you describe all of this makes me want to work with him because this SOB is going to be rich and win a Nobel or two and I want to be around that, at least for the hot girls