How is it possible that the Magento core is Deprecated?

It’s been a month since I received the assignment to create a simple redirect payment method, while I had no previous experience in Magento, so obviously, I am trying to find the latest documentation to do this as close to “best practices” as possible.

I have failed to find an up to date documentation, so I decided to “check how the others do it” as it has been suggested to me both here in /r/magento and in the magento stackExchange, so I did just that.

Welp…. The core Magento “Bank Transfer” and the rest of the core implemented payment methods are already deprecated.

How do you **realistically* write good code in Magento?