I am not going to comment on the chrome only and non standard API complaints.
The key insight behind modern mobile messaging that allows them to scale cheaply is that for most consumers the phone is persistent enough that the server does not need to store messages. Ask a 19 year old if they need their old whatsapp messages. Most will say no. In fact, many proactively delete them. Turning a mobile messaging into a CPU and bandwidth only problem is a clever hack instead of it also being a disk and indexing problem.
This is hard thing for a lot of us to understand because we come from a world where our business has message retention and surveillance requirements. We want to run quantized self and sentiment analysis reports for the last 10 years. But most people either don't know that might even want that.
The other key insight is that knowing the user's identity can be more important than the user themselves.