The WCO is a variant of the vertical offense. It was developed by Walsh out of necessity. Walsh didn't have the personnel to run the vertical offense when he got to SF. Walsh was trained by the original operator of the VO...Paul Brown. (Sid Gillman did make the VO much higher octane)
So while it is called the vertical offense it isn't always so vertical. In truth we run a good number of drags, ins, digs, outs. shallow crosses etc. The misconception about the vertical label is that does require two WRs who can go vertical running deeper routes. But it also requires (or used to) running between the tackles and needs routes to the TE or RB. Walsh's offense was mislabeled by the media and it just stuck. The WCO is just throwing it short because you don't have time to develop deeper routes because you either don't have the WRs to run it, can't get people to bite on the run to throw the deep ball and/or have an OL to give you time to throw longer routes. Does that sound familiar to anyone and I'm not talking about me bringing this up from time to time.