This argument is as spurious as the frames of reference and definitions needed to support it are extreme. Also the orginal post didn't say there were no flaws with "simultaneity", just that calling it "wrong" was "wrong." It's well known that any causal relationship is preserved from any frame of reference, and furthermore "events" on the macro scale don't happen at a discrete moment in time. If you have a balloon with a chipmunk suspended inside it, and you release the chipmunk so it falls and pops the balloon, it can be said with perfect accuracy that the baloon popped simultaneuously with the chipmunk falling, assuming the balloon was not on a table and the chipmunk continued to fall past the edge of the balloon.
The arguments against "simultaneity" require the precise scientific definition of the term, which should be confined to academic papers.
Do not try the above experiment at home.
The general gist of the matter is it would be technically possible to "synchronize" these clocks in the sense that with enough external data to accurately determine the frames of reference involved, we could know the time on one of the clocks as observed by an individual next to that clock from the value of another a clock next to us, even if that individual could never tell us the time on the clock because by the time any communication reached us, it would be stale. This despite the fact that the clocks are actually running at different rates on most frames of reference, not just different offsets. If that was done bilaterally, and both calculations yielded each other's input value, both parties could agree that, in retrospect, they read the clocks at the same "time".
An external observer to both clocks might see the readings happen at different times, but if they have any intellect they have to account for their perspective not being the only valid one.
It would also be possible to construct an average aggregate clock out of a group of these, the question is merely the utility of such a clock, since instead of a "timezone" you'd have a "framezone" where you'd have both an offset and an ongoing drift, not to mention the parameters of that adjustment would not be constant because phenomina like shifting planetary crust don't play nice.
We would not be able to measure the speed of light without such systems, so they obviously play an important role.