Both tools are necessary for fast engineering, but in different contexts.
A lot of developers have this preference for client side code. Since the early days heroku has been building the client side bundles for rails.
Uploading source code is a dealbreaker for me because I do not trust Google or myself. Google probably has language in their terms that they may do whatever they want with anything you upload to them.
I also do not trust myself to properly configure security parameters around this with the risk of leaking source code.
Binaries are a great strength of Go. Too bad this platform doesn't use them. I will take a peek at the new Container platform that they are building, but that sounds more heavyweight, which probably comes with a higher price. (I have not seen any actual pricing)