Actually, I am not so sure you get as many direct routes out in the Southwest of the USA when IFR as you do in the mid-section of the country, especially at non-O2 altitudes. There is lots of military airspace here...and a few tethered balloons that go to 14k or so...so most typically one gets airway routings when IFR. For example, IFR generally won't let you fly thru MOAs even if they aren't active. One good thing about some of the IFR low altitude airways in the Southwest is that they allow you to avoid big rocks and generally seem to follow near some of the interstates (but not the part of V94 from SSO to TFD or GBN to BLH or along V64 just west of TRM). OTOH, most of the time it is VFR here so you get lots of desert to look at!
Btw, if it is your first time to Southern California (in a plane with you at the controls), you can expect it to be somewhat busy on the freqs and lots of frequency changes in rapid order. KSNA has a mix of GA, corporate, and airline traffic...but SoCal Approach and the SNA tower do a marvelous job. If you were to get any IMC at all in the Southwest, it would likely be a coastal marine layer at KSNA in the morning hours. On the other hand, there are many days in SoCal when the haze is so thick you'd swear it was IMC...!