Google will stop using Inbox
In both cases it was not successful, because Google has focused too much on itself and completely ignored the problem of interoperability.
The power of e-mail is that it works everywhere and at all and that there are hundreds of client and server programs. You can not replace something like that with one web client. Apparently, Google’s vision is that e-mail should be destroyed and that is a good reason not to park e-mail at Google.