Then they introduced Gatekeeper, but you had the option to disable the Gatekeeper check for all applications.
Then they removed the option to disable the check for all applications. You now only have the options "App Store" and "App Store and identified developers".
They have definitely made the whole thing harder and harder during these past 10 years. Now if you don't want to pay Apple for a developer license, or you're just otherwise ousted by Apple (like Epic Games), you need to teach your users on how they can circumvent Apple's restrictions.
The courts have agreed that the reason their apps are not in the store is of their own doing, which is why they have not granted an injunction.
Whatever the outcome of their case, they are not an example of some general trend of Apple ‘ousting’ developers.
The first time you "RMB -> Open", as you put it, it won't allow you to open the app at all. You have to do it twice, only the second time does the button to actually open the app appear.
Both times the dialog boxes mention "malware". Both times the default button is "move to trash".
In what way was it made "more difficult" than that?
What exactly suggests it is "becoming (even?) more difficult"?