Waze has utilized service roads well for me in Queens NY - they can be noticeably faster than the main freeway - but that's for short trips, only about 10 miles. I have two speculations about the routing algorithm:
(1) It doesn't deal with a fine level of complexity until you get close because it doesn't want to take traffic into consideration for the whole distance. Once you get close it's willing to do so.
(2) It has a rule about using freeways on trips above a certain rule-of-thumb distance; once you get below that distance it is free of that rule.