There are already lots of calendars if one cares to look. Why bother with a 7 day week other than the biblical mandate? Why not use a lunar calendar? It would certainly simplify 'calculating' Easter. Having a leap day is a lot less intrusive than a leap week and does anyone actually bother to memorize the Metonic cycle? Is it because lunisolar calendars are uncommon or because they're a pain or both?
I think having timezones benefits us in the sense that we can say "It is lunch in city A when it is dinner in city B". Knowing when people are likely to be sleeping/working/playing in different places helps more than having One Timezone. Pilots use UTC because they're between timezones too much for them to follow a 'standard' schedule according to our approximations of the Sun's movements.