The Date API is fine and relatively normalized. Once you understand it it's very easy to work with. It's biggest problem is that it simply does not support timezones, which is the main reason to use Temporal.
It's simple. In it's simplicity it left many features on the floor. I just can't connect with the idea that someone would need to constantly be on MDN in order to work with it. It's not so horrible that it defies logic.