Ziggs does not need to execute towers at 35% max health
If he really needs to execute towers, I can get 5% or even 10% max health, but when it still has over 1/3 of it left? No! No one needs that. Especially in the Bot lane with its paper mache tower (I know he needs 5 ranks in it to get 35% but seriously, it starts at 25% max.
Also I am pretty sure this is similar to the reason why the W tower damage was removed on Azir.
all have ways of taking towers that is on par with his execute