Robert,
I agree you view, but it has a horizon. Beyond that anthropocentric reality is a greater truth.
Consider your sinusoidal wave travelling the empty highway at c. It traverses d/t wrt the rest frame of the highway. No problem, but of course it can't then be 'measured'! The moment we add a bunch of electrons to create a detector, then the wavelength (so frequency) they find will be that ON detection, not those 'prior to' detection. That is the point which human intellect has so far failed to see. Detected frequency IS then observer dependent, and is then always c/n in the rest frame of the detector.
Once you've got your head around that, we then need to 'back off' and take an overview from out in space. What if there are TWO similar planets, both with empty roads, but rotating in OPPOSITE DIRECTIONS! If we could 'see' the moving ('propagating') waves we would then see two DIFFERENT cases of c. Ergo c and the c' which many (Tom for instance) denies!
What reclaims logic and the SR postulates is then applying the first lesson to the second case. Al light interacting with our lenses or antenna WHEREVER we are has been instantaneously modulated to the new LOCAL 'c' in preparation for measurement.
Very few have taken the 'slow down and think' path far enough to be able to rationalise the initially complex and unfamiliar dynamics. I believe you've glimpsed them already in parts and have great hopes that you'll manage to put them together.
Best wishes
Peter