Value of Time and Thunderlords vs other masteries
My idea is practically common sense, and can be illustrated best by relating Thunderlords to money. Getting $100 now, for many reasons, is worth more than having to wait for $100 later. So if anyone asks me (or anyone) if I want $100 now [Thunderlords], $25 a month for 4 months [Deathfire], or a compounding $5 i can pick up everyday for 5 days [Fervor].... I (along with everyone else) will take the $100 now.
In a place (LoL) where every second of action is priceless, a ton of interest (i.e. damage) would have to be added to account for the value of time. I really do believe this is all common sense, and since it applies to everything in the real it would be good for the game.
The instantaneous application of the damage is why Thunderlords is head and shoulders above the rest.