Ah, I missed that.I see where you're coming from. I drew it as the two sections of 3" to be on top of one another so SH3 could come directly into the side. Caveat of the perspective I'm using.
Except SH3 can't come into the top of a wye--the vent connection has to be within 2" of fall from the trap outlet, so it needs to enter a horizontal wye horizontally. The vent connection is the 2" double lav drain coming in.Your method with the 3" side by side makes more sense so there are fewer bends and SH3 comes in from the top into a wye. That uses 1" less overhead height as well.
What you could do is pitch the barrel of that wye a bit extra so that by the time the 2" line hits the WC3 line, it has dropped to the same elevation as the WC3/main line. Or go with what you drew, in which the short section of WC3 line parallel to the main line doesn't have to be directly above it, just parallel to it.