I agree. Another math breakdown.
Late game Lux in teamfights with 600 AP (we will assume shes level 18 with that much AP).
Stats on keystones with 600 AP:
DFT 8+150 for 158 damage over 4 seconds, reduced to 2 seconds for AoE abilities.
This means if she were to land and E on ALL 5 enemies that would deal (158 divided by 2 is 79 and 79 times 5 is) 395 damage for her keystone DFT.
TLD is (10/level) 180+60 for 240 damage, which actually can AoE but we will disregard that.
To compare to DFT, Lux needs to get that 79 damage/target on at least 3 targets in a teamfight, then wait 2 seconds, for the damage to become equal to TLD upfront damage. Or wait 6 seconds with two more ability cast to reapply the DFT damage on one opponent.
Of course that extra damage may mean the difference between a marksman, mage, assassin living long enough to kill you or another carry... I mean its just 2 seconds you have to wait is all. TLD improves Lux 1v1 considerably, and in teamfights that last long enough to do less damage than DFT you have to ask will TLD put an enemy down faster so they lose carry damage output in said teamfight?
It was never a question of can DFT WORK on Lux. It was a question of why are you trying to slowly kill people with a nuker? DFT is my go to on Brand. Every match its DFT, Brand passive, and Liandrys Torment; 3 DoTs suck it!!
Also people need to remember what started this line of discussion is that I asked someone why they didnt have TLD on a Lux. They didnt respond with "Well based on my match up my best shot is to poke them out of lane and reduce kill pressure on myself. So I took DFT. Its a play style preference also." NO, they didnt say any of that. They said "Thunderlords doesnt work on Lux." That is fucking stupid. A matter of preference, meh, ok, fear of the match up so changing approach, fine. TLD DOESNT WORK ON LUX!? No, thats just dumb, and someone that dumb doesnt need access to a button to label others unskilled because theyre too dumb to use it properly.