FWIW, I've never had a PCM-controlled starter work right. Even in Porsche Cayennes, they would sound horrible sometimes, coming back into service for the same problems as listed above.
Believe it or not, some of the "problems" are actually better on the engine, and why the PCM causes the problems. For instance, in the Cayenne, the PCM uses sensors to see if the engine should ignite the cyclinders immediately, or allow the crank to crank a few cycles to "wash" the internals first, then ignite. What will happen is that the engine will crank a couple times, then start. It "sounds" like it's not starting, but it's actually running a couple crank cycles then starts. I had a prelube system back in the 1990s that did the same thing.
IMHO, there's alot more going on inside the G6's system which is why sometimes it does not immediately start.