Either way, not much difference
Quite honestly, seems like big difference to me. O_o
In your suggested way, any damage that is "less than your preset value" leaves you with unused Reaction ... and that is the problem.
If you would decide when to use it, and when not ... all you see is Ragzlin attacking you ... you can use your reaction and avoid dmg 2, or dmg 22 ... that is just how thigs go.
Now imagine you are Tiefling ...
When your preset system automaticly avoids reaction for any damage that is less than 10 and therefore "not dangerous for you" ... you can easily use Hellish Rebuke, Tieflings inherit in any turn ...
Maximal effectivity, no place for misstakes ... either you avoid killing blow, or you hit back really hard ... and you didnt basicaly do anything, the game did everything for you.
When you have no automatic system, but only popups ... YOU have to gamble, you have to decide, and then (and only then) you find out if your guess was right, or wasted.
That is huge difference. :-/
