There are two factors here, both of which will limit you.
The first is the solubility of caffeine in water. Paparazzi found it for room temperature, it is going to be higher for a hot beverage, but whatever it is, it is a hard upper limit. So, if you were to drop a tablet of 1 g pure caffeine into 100 ml water, and a tablet of 6 g into another glass of 100 ml, you would only get 2 g of caffeine from drinking the second water, not 6 g. But that's unlikely to matter in real tea making.
The second one is the extractability of caffeine from tea leaves. I am not going to do any back-of-the-envelope calculation for that, but basically, the amount of caffeine you can extract into the tea depends on the concentration of caffeine in the tea and the concentration of caffeine remaining in the leaf. The less concentration you have outside the leaf, the more can you get from inside the leaf to the outside. In practical scenarios, this is going to limit you much earlier than you hit the caffeine solubility problem.
It is impossible to predict how much the difference in extraction will be. Somebody with a scientific computing background and access to the right formula and hardware could make a model for a given tea making recipe and a given leaf, but a recipe which uses different time, temperature, and a different plant will end up with a different factor. The best we can say is, there will be a difference (it won't be the same amount extracted), but it will be noticeably less than 3x the same amount.
This goes for basically anything you extract from the tea, so also EGCG.