The problem with you argument, and all the other ones like it, is the fact that they are all the same. You basically argue that any release schedule that isn't the 5th edition one is automatically the one they would use for previous editions. If you actually compared the current one to the earlier ones you have a lot of room for a happy medium, unfortunately the current one just doesn't hit it for a lot of people.
You say that again and again. And
again. But you've yet to ever say how many books this mythical "happy medium" actually is.
Because the current schedule
IS a happy medium for many. Three books a year, two of which just providing encounters and monsters and not bloating the game. The third offering options and lore.
That's pretty good compared to just one book a year. Or one book every two years. Or no books at all.
Unfortunately, DMsGuild has a lot of crap you have to sift through and loads of DM's plus sanctioned games do not allow DMsGuild stuff so what then?
Talk to your DM until they let you use the content.
Find an author or publisher you respect and use just their work. Branch out when needed.
Revise the content with your DM until it is acceptable.
Or all else fails, make it yourself. And then sell that on the DMsGuild for $$.
What you could easily do is when you do a race specific book, have about four or five races listed in the book so you cover more people with in one book, same could be said for classes. You could do a martial handbook, a rogue handbook, and a spellcaster handbook.
And how big would these books be?
WotC is currently publishing hardcovers only. The smallest they could do that is probably around 96-pages.
If you do a book with 5 races, that's almost 20 pages per race! And if you do one on "martials", even if you include the ranger and barbarian that's around 32-pages per class. That's a
ridiculous amount of content when a subclass takes 1/2 to 3/4 of a page. Can you think of 30 different fighter subclasses?
Plus, even if they double their splatbook release schedule, that's still two or three years to cover all the classes. Who wants to wait three full years for their class to be covered?
And then what? When you have 30 subclasses for each class you have enough content forever. That's more content than any gaming group will every use. The edition is done. Nothing else needs to be published.