Thresh as of patch 3.10 will gain flat 0.75 armor and ability power instead of starting at 1 then having diminishing return for every subsequent souls. It is definitely a nerf during his early game, but when exactly does he surpass the old Thresh (not accounting for his hp nerf :P)? So here is Soul Number comparison between the Pre 3.10 patch Thresh and Post 3.10 patch Thresh.

Magic Soul Numbers:

Number of Souls of required to have the same amount of armor as the old Thresh (past this number you will have higher armor than old thresh): 125 souls (105.75 armor at this point)

Number of Souls of required to have the same amount of ability power as the old Thresh (past this number you will have higher ability power than old thresh): 101 souls (75.75 ability power at this point)

Number of Souls at which New Thresh will gain more armor and ability power per soul than Old thresh: 52 souls

Number of Souls where there is highest difference between the total armor of new Thresh and Old Thresh: at 50 and 51 souls with the difference of 12.375 armor (61.875 armor on Old Thresh and 49.5 armor on New Thresh)

Number of Souls where there is highest difference between the total ability power of new Thresh and Old Thresh: at 50 and 51 souls with the difference of 6.375 ability power (43.875 ability power on Old Thresh and 37.5 ability power on New Thresh)

Although Thresh does have potential to be stronger now than before, looking at the number of souls required to reach that point (125 souls) it is a definite nerf. Most support Thresh do not even reach that amount of souls in average game. Thresh however, did require a slight nerf since he is one of the most sought after support in both competitive and non-competitive games. Combined with the base health nerf Thresh will die in 1 less auto attack from ADC and 1~2 less auto attack from support, leaving more room for counter play against over aggressive Thresh during early game. Personally I think the nerf is just about right, what is your opinion on it?