Theme workflow balance is combination of several factors:
- amount of code, individual to sites
- amount of code, shared between sites
- incorporating upstream changes
Each of these can be important and each of these can be unimportant.
Parent theme model satisfies all of these reasonably well, but not very well. You get clear separation of shared and individual code, as well as straightforward upstream updates (if using third party parent theme). It start to come apart when any requirements gets larger than usual - a lot of individual code or a lot of shared code that can't be easily mixed in third party parent theme.
Starter theme on other hand is very specialized model. It favors individual site, but disfavors upstream changes and shared code. As soon as you make starter theme your own - all burden of moving code in and out of it is on you.
The newer trend is separating frameworks into plugin-like component rather than them running parent theme completely. If you are acquainted with Hybrid as parent theme look into Hybrid Core. This approach is essentially improvement on top of parent/child with upstream updates made easier by being limited to framework and not whole theme.
In a nutshell (gets a little subjective here):
- starter fits individual sites
- parent/child fits multiple sites with not much customization
- framework/parent/child can adapt to anything and everything, but is also more involved to develop