A 23 overhead that combos isn't that bad, although according the frame data the proration is pretty bad (not entirely sure how damage proration works in CP). And now that it doesn't have the first hit you can use it during blockstrings as a legitimate overhead. Tao's 6B is slower (26F) and Haku doesn't get anything off his 6B at all.
Put honestly, all of that is moot compared to my original point: You're a heavy zoning character, you don't need a low-immune 4B on top of full-screen laser blades.