Isn't it true though that you'd want to react as fast as possible to that change? Not have some average which you can't accurately know when to mine and when not to.
Not really because while it may go down, it will likely bounce back up right away. Unless I could forecast what will be the average over the next block (or set of blocks), instantaneously looking at the difficulty is not accurate at all since it will change almost as soon as you look at it.
This makes TRC hard to gauge in any way, unfortunately.