I think its important to separate out Joplin users from forum users. The vast, vast majority of Joplin users will never become forum users no matter what happens on the forum. And as I said above, I don't think it's a good thing if you have to join a forum to be able to use a piece of software.
Also, I don't think it's the volunteer dev's obligation to answer newbie questions. And I don't see that happening here any way.
The thing I do see frequently is new people coming in and (without searching the forum) asking for a feature that has already been discussed at length and rejected by the devs. I don't think that reflects the majority of either new Joplin users nor forum users. But it does tend to generate a lot of heat. Most new users have never used FOSS before and don't understand that coming here with whiny rants isn't going to accomplish anything.
Of course on-boarding could always be improved. But good software shouldn't really need on-boarding. It's just a note taking app after all. Perhaps the problem is that a percentage of people have never used a dedicated note taking app and expect it to be like a word processor. But having a sub forum for newbies won't fix that.
In my opinion, subforum is not a must but it is worth attending. It is a speedy solution when compared to meeting the same goal using the original forum. Because the main problem is the atmosphere, if using the old forum to implement that, it means you have to change all members' minds first.
4.6k registers and 484 fans, I think it is not really bad, but I just wish people would pay more attention and think about how to reduce the gap between them.
But a forum can be the lower-cost solution overall, I think it is suitable for promoting an openscurce project. When I talk about the cost, I also consider manpower and time. One of the advantages of a forum is most of the time users can service each other without you. Your main responsibility is just to create a good topic for them sometimes and find out which post you should follow and reply to. If maintain great there are always can give you many surprises, and most of the surprises usually come from a newbie or a younger one who uses your software and services with only emotions, when they feel happy, your product will be the king of the world in a period.
This is a classic problem in the FOSS world and those who have solved this problem have basically tended to come up with something along these lines:
Sensible defaults
Wiki/FAQ/Documentation for full or authoritative answers
Forums and mailing lists for troubleshooting individual problems and development
Search before you post
When people complain about Newbies, 9/10 times it is because Newbies are asking something in the documentation or something that has already been asked. Thus time and resources are not spend solving the problems but helping people search for existing materials.
The challenge here is that you want to use the opportunity to train the newbie how to solve their problem without asking in the future without totally driving them away or being rude about it.
Take for example if you can't start your lawnmower. The first time you call your dad and ask, he can just tell you, but if you call him and ask every time you mow, that is disrespectful because it should be your responsibility to remember or take notes. But if a forum is full of people asking the same question, that irritates people.
Personally I think the Joplin forum is healthy and doesn't need to change.