The big downside of AWS: to difficult to use for many. It seems to me a new entrant which combines easy of use, embraces opensource, would have a good chance in the market.
+ Rackspace. But like many these don't come from the cloud market and still think in terms of servers mostly.
Presumably you are talking about Google App Engine, which is just a small part of GCP. Amazon's comparable offering is Elastic Beanstalk. The core building blocks on GCP and AWS are the same: raw virtual machines you can build anything upon yourself, GCE vs EC2. GCE has been around since 2012.
Google has a lot of different things as part of it's offerings.
but very quickly:
Google App Engine = google handles as lot for you. not a vm
Google Compute Engine = vm's plus an easy to use interface
"Google Compute Engine delivers virtual machines running in Google's innovative data centers and worldwide fiber network."
Azure is the other major option.