tl;dr: think of the newbies!
Couldn’t this up here apply to this down here as well?
What I mean is, the same way you think self-correcting would be easy for someone hitting Hard too much, shouldn’t it be easy for you to overcome the “Forgot” aversion as well? Everyone has preferences, but I think helping those less technologically inclined or those with less patience should be the priority for an app. I’m sure most people who even come to this forum are not in these groups, though. In any case, I believe if there were only two buttons by default, this discussion wouldn’t be necessary, since “Again” and “Good” would be clear enough.
I think you overestimate people’s power of attention and patience. As I said above, I don’t think taking ourselves as standard users is a good idea. I can assure you of all the students I have taught how to use Anki ever (dozens), probably next to none of them have ever opened the Deck Options or installed an addon. And if they have taken a look at the time intervals, it was probably for the worse. Time intervals can be very misleading (a user can think something is too long or too short and therefore press another of the buttons instead of the one they should, misjudging their memory ability and interfering with the scheduler’s job). I actually think intervals should be hidden by default (but that’s probably better left for another thread).
Again, I would kindly ask everyone not to take design decisions thinking of power users (unless that’s the main target of the app, which I think it’s not, but I might be wrong). I really believe these decisions should be geared towards making it easier for newbies to get aboard, using an addon is not very newbie-friendly (I have students having problems understanding “decks” and “shared decks” or asking me to “add more cards of X type” to a deck they’ve already installed, as if I could update them remotely just to give an example).
Also, not changing things because they’ve been done like that for a long time or for fear of what could happen is not conductive to improvement. Sure, maybe not changing everything at once is the better path, so people can adjust progressively, but that doesn’t mean not changing. Existing guides will be revised anyway and, otherwise, they will be superseded by new ones, that’s completely fine. This has happened before (FSRS, for example) and will happen again. I don’t see how tradition and habit are good enough arguments to keep a system that might well be causing more confusion than not.
I’m repeating myself here, but most users don’t have the patience to read the documentation, come to the forums, read tooltips, troubleshoot, etc. They will just try what’s instinctively reasonable for them and if it doesn’t work, they will just give up and stop using the app.
Notice that the opposite won’t happen that easily. A user capable of patiently reading the documentation, asking in the forums, installing an addon, diving into the options and preferences, etc., won’t really be immediately discouraged if they need to change a new toggle in the Preferences.
Sorry for the long post, I wanted to share my thoughts on the issue.