Funny that you mention Unity because they first had an immediate mode UI that was very difficult to work with, then they got a more flexible UI but decided to go the HTML way of having separate documents for elements and styles, making the whole design process way more complex.
The new input system is powerful and flexible but is slower to learn and makes lots of things that used to be easy much harder.
Same for the new UI Toolkit and several other recent additions. I think it's a company culture thing - nobody internal is rooting for casual devs or noobs.
The problem is - everyone is a noob on something. You might be an incredibly experienced Unity dev who rarely touches input or UI. You want to quickly implement something and you're going to feel the pain.
"Make the easy things easy, and the hard things possible."
Approach it like that and you have a slight fighting chance because you know what you are getting into.