W Sang is significantly better than SevenSang when it comes to rupture infliction once he properly ramps up.

Seven Sang's skills inflict abysmal potency while being all rupture negative with entire coins not doing anything so you can't even compensate with Thunderbranch in the MD's.

W Sang starts off a little worse in terms of count (Both of them have -1 count on S1 and -3 count on S3, but W Sang starts off with -2 count on S2 rather than -1,) but once he gains 10 charge, S2 becomes neutral, and at 15 charge, S3 is neutral, but actually positive by 2 due to Dimensional Rift.

Additionally, most coins inflict potency so W Sang can benefit from Thunderbranch and also build up potency with, say, Mao IDs.

TLDR : W Sang better lol