AssetBundles. Not marked as obsolete. Not marked as deprecated. Unity docs look fine, with no references to anything else you should do: https://docs.unity3d.com/ScriptReference/AssetBundle.html. They are in fact obsolete anyways. See here: https://learn.unity.com/tutorial/assets-resources-and-assetb... "this tutorial has now been deprecated. We now recommend using Addressables for your projects"
EditorUtility.SetDirty(). Rider says "Marks target object as dirty. (Only suitable for non-scene objects)" and it's not marked obsolete or deprecated. Seems fine, right? Nope, it's been deprecated since 5.3. To their credit, the full Unity docs do reference this, but who is going to consult Unity docs for literally every Unity function they ever use, in their entire project? It should be right in the IDE. Better yet, the function shouldn't even exist! Unity 5.3 came out over 5 years ago!
I can see that's a gray area (you are kinda deprecating it by doing this) but the strict definition of deprecation probably involves a pledge to remove that feature in a certain timeframe.
I'd be much happier to bitch about the stuff Unity has officially deprecated without having a good timetable for a replacement (Networking, Real-time GI) or done a terrible job of communicating the situation (Steam VR is "not officially supported" sounded pretty apocalyptic whereas it turned out to be not quite so bad - Valve had taken over responsibility for support and their solution was released to beta with a month of the doom and gloom corporate-speak announcement)
I've always thought that that is deprecation, but I could see your argument that it's not.
Fortunately I haven't had to deal with the officially deprecated features without a clear replacement. I can imagine that would be very frustrating.
You might have to use a superseded feature because you're maintaining old code. If Unity cares about backwards compatibility (admittedly, I'm not convinced they do), they need to keep supporting and documenting the old features even as they nudge you away from them.
Honestly most of the criticisms you've gave are you not understanding how something works - like GetComponent. I do agree with you on 'null' though! And how Unity uses it. I think that decision came from them trying to make it more beginner friendly to deal with destroyed/removed objects when it first started - then they had to live with it
Perhaps you should explain how I've misunderstood GetComponent.
The best practices that have sprouted up around GetComponent say "Use GetComponent<> only in Awake(), and don't use AddComponent or RemoveComponent at all." But once you start following all these best practices, you've lost all the benefits of having GetComponent be dynamic in the first place. So just enforce it at a code level, and give me the benefits of static typechecking and compile time errors when I screw things up.
Are you sure? My IDE (Rider) shows gives me a tooltip for any methods that Unity has declared deprecated. There's also console warnings and big notices at the top of the docs.
Package Manager also clearly marks certain packages as experimental or deprecated.