The article is almost entirely the answer to your question.

> there are risks when you go down.

Solved by SMTP on protocol level. With HTTP, must be solved on both client and servers application level.

> webhooks are ephemeral. They are too easy to mishandle or lose.

SMTP has this baked into its heart. Loosing messages is possible, certainly, but rather hard to do. With HTTP, it's really simple.

> In the lost art of long-polling, the client makes a standard HTTP request. If there is nothing new for the server to deliver to the client, the server holds the request open until there is new information to deliver.

SMTP is push, not polling. So all those issues are solved for you.

> SMTP is push, not polling.

Yes. And if you want to poll, POP is polling, and IMAP has both polling and immediate notifications.

Yes, but SMTP is a protocol wherein a system opens a connection to another system and says, hey here's a message.

And if that doesn't succeed for some reason, it reliably queues and retries.

That's a push.

I was not disagreeing, merely providing additional information. I have edited to clarify.