During the War of the Shadow, the use of balefire had a horrible effect on the pattern. Whole cities were burned out of existence and the pattern was almost destroyed before both sides decided not to use it anymore.
Considering the fact that the Dark One prefers chaos, why would he (or his) care for the effects of balefire? Once resurrected, the Forsaken are quite free with its (albeit limited) use. Moreover,
In the last battle, Demandred and Mazrim Taim go nuts with its use amplified by the sceptre sa'angreal.
Something does not appear to compute.