It is certainly my gut feeling that Amazon is evil as hell but I think that I'd really like to see an actual investigation by folks who study this stuff to know whether Amazon was using their pricing predatorily or not. People, especially executives, are dumb - there's bound to be an email somewhere about John congratulating Fred about managing to shut down Plug's Stuff Hut a small family business if that was the intent and these actions were being made to accomplish this goal.
However, I thing that your last point is not relevant. What-about-ism has no place in the law or it necessarily creates a slippery slope. If Google is also able to do this and purposefully did it in a predatory manner to accomplish a market advantage they both need to be legally pursued - and GCP not succeeding doesn't necessarily mean that Google didn't try underhanded actions to get it to succeed - it either means those actions weren't enough or they were incompetent (but still malicious). Either way each case needs to be judged on its own.
However, I thing that your last point is not relevant. What-about-ism has no place in the law or it necessarily creates a slippery slope. If Google is also able to do this and purposefully did it in a predatory manner to accomplish a market advantage they both need to be legally pursued - and GCP not succeeding doesn't necessarily mean that Google didn't try underhanded actions to get it to succeed - it either means those actions weren't enough or they were incompetent (but still malicious). Either way each case needs to be judged on its own.