Yeah, that was one of the studies I read on the topic. (The key part is "Caffeine concentrations in white, green, and black teas ranged from 14 to 61 mg per serving (6 or 8 oz) with no observable trend in caffeine concentration due to the variety of tea.", although they bought mostly black teas and not many white/green or any oolongs; but the other studies don't show a clear trend either.)
Did you see any data on natural variability -- that is, compare the caffeine content in tea from two different bushes on the same planation; from different plantations (on different soils, different altitude, etc.)?
What makes tea white/green/oolong/black is just post-harvest thermal processing and it seems likely that the caffeine content is determined at the plant level.
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