I've got nothing against stateless tokens. What I'm saying is that it can be a much easier and more effective pattern to add a second layer of security than to add complexity to the first layer (the token). I believe this is like the idea of defense in depth. For example, making signed-in users re-enter their password before performing certain actions may be preferable to introducing cryptography into all sign-in actions.
This isn't just for all sign-in actions.. it's for all API requests, and in some designs passthrough requests on behalf of a user to another server/service. It isn't just used for UI requests. It can also be used from Server to Server/Service requests... across data centers. You can do signed tokens/authentications without introducing many potential points of failure.
If you're on Java and using an ORM like Hibernate, then that user will be found in the second-level cache. This will eliminate the need for a database roundtrip for all requests after the first authentication. From that point on that particular user will be retrieved from memory.
Which will require session pinning for the load balancer, not to mention, I'm not using Java or a similar ORM. That will only help for a single instance of an application on a single server... not much help when you specifically don't want session pinning.
I agree that not everyone is on Java and using an ORM. But is it only useful for a single server? If you have multiple servers then you would also have a distributed second level cache which would eliminate the need for session pinning.
distributed, or duplicated... each server potentially making that DB request... depending on load adding at least 2-3ms, potentially more. If a given request to a single endpoint needs to touch a dozen more, not including resource lookups and when not everything is parallel... or across datacenters, from the colocated to aws, etc.. it all adds up.
Very short lived JWT mitigates this as the window for replay is reduced, over HTTPS by the time you can crack it, that window is effectively gone. The server can verify a signature on a JWT in a fraction of a second... far faster than a DB call... Not including replication issues.
This is as opposed to < 0.1ms for verifying a JWT. JWT is a structure for stateless tokens... once you have a token, what does 2FA add? nothing. Also, some algorithms are insecure, so don't use them, or blacklist them... Or, better whitelist the algorithm you do use.