I remember reading somewhere that caffeine technically doesn’t act as a traditional stimulant. What it does is block some sort of chemical from registering to the rest of your body that it’s still tired. Unlike coffee, which sends more of these little suckers to damn up your “ZZZzzzzzzzz”-s, tea-..uh…-ine is time-released, thanks to those lovely little tannins.
But take this with a grain o’ salt (or sugar) and read up on it yourself.
The theanine mitigates the effect of the caffeine, from what I understand. Coffee has nothing to regulate the caffeine’s effect and that’s why it has more of a hardcore wake-uppineess about it. You still have to factor in for habituation, personal metabolism and psychology though, I guess