Good points. Not like all the gear came from a single "factory" near Rome. I would imagine that there were "vendors" all over the empire that would build/make according to a basic spec or design template.
How about variations in "clothing" along with the kit? The image of a soldier with a tunic and bare legs doesn't much pass the logic test for a January patrol along Hadrian's Wall. It would seem to be a bad idea in the middle of Tunisia too - when in North Africa, do as the North Africans do (and cover your bare skin).
How much was the Roman army willing to adapt to local conditions when it came to establishing what the standard for that duty assignment was? Was it, "Okay men, I know its hot, but we're Romans and we wear our armor uncovered even when it means it will get so hot that it will burn out skin to touch it!" Or was it, "Okay men, I know its hot. So we've decided that you can cover your armor with your cloak to keep the sun directly off it."
I served in the Army many moons ago. Each day, the senior NCO would set the "uniform of the day". But... there wasn't much wiggle room for him to vary things much. We weren't issued shorts - and therefor didn't wear them, even when it made sense to wear shorts. BUT, if you got shipped somewhere far away with a much different climate, your "kit" could vary, Temperate vs. tropical vs. polar.