It's not irrelevant, if return style was a problem every car that has that system would have fuel quality issues. (as there are many that absolutely need premium fuel octane)

Yes, dead heading heats the fuel in the rail, so it's still running on hot (hotter than return style) fuel 99% of the time until it gets flushed out with enough heavy throttle usage.

There are downsides/upsides to both.