What is the point of a shower diverter?
What you need is a valve designed just for shower only. Not a valve assembly with a diverter, which are specifically designed for tub/shower combination:



No diverter here, most any manufacturer that you have seen offering the tub/shower valve sets also makes the shower only units. To answer your question, the point of the diverter valve is so you can fill the bathtub without water spraying on you out of the shower head.