That's even worse than I imagined... Why on earth would they choose to do it that way? Wouldn't it have made more sense to just do the commercials on the West Coast?

Color was just an improvement on the existing BW network going from NYC west as it was built after the war but it was not a NBC/RCA/CBS/ABC/Dumont network. It was the monopoly of AT&T Long Lines and all of their charges for transmission to the local stations. Coaxial at first and then microwave along with improvements to local stations on the net to pass color.

Why build two network controls when one would do? It was analog, proc amps all along the path to keep the signal good and NYC had all the resources for the full network. And ad agency contracted announcers for any given refrigerator commercial could not be on both coasts. These were the day when ad agencies ruled. No need to keep a second crop of announcers, staff, studios, film, stagehands, et al in LA. Just use two one way paths. NYC was the center of the universe.

LA was perfect for talent, studios and shows going east then back west. Let NYC do the heavy lifting going west.

When I got in to broadcasting in 1970, AT&T was still pretty much the same one-way system. NFL on Sunday via CBS was an adventure to get on the air with early and late games. There was a closed-circuit AT&T show on Fridays on CBS after the afternoon soaps with a bunch of engineer types with thin black ties documenting all the switches and patches that needed to be made for any Sunday for the markets and time zones.

There are some very interesting wikis on telco multiplexer/de-multipexers and tech going back to the beginning. It is fascinating how many calls they could fit down the same line with the Network video link, how many they could without video, other services that most consumers never saw (directly) etc.

They had to develop IIRC phase delay equalizers to compensate for color distortion from the long lines transport.

In terms of how much tape itself degraded the TK-41 output, I would say that a keen eye can differentiate which degradations come from where. The main TK-41 limitation was signal to noise ratio. Tape could contribute things like moire patterns in high chroma areas (on the low-band machines), or head banding when the four individual heads did not match, which could show up as hue shifts or differences in SNR, but would be identifiable by the different bands in the picture. Other tape issues could be edge effects like ringing or overshoots due to the sharp filters in the tape machines.

Most of the degradations you see on youtube come from multiple generations of other tape formats through which the material has come down to us, and/or digital artifacts due to insufficient bit rate.