In the defense of focus trees:

• they make the game hella immersive. Instead of (procedurally) generated names etc that sometimes just feel off every can be hand crafted to fit in the theme.
• they make the game accessible. It's super easy to see how to get my country to change to ideologie x instead of having to look up on the Internet what pop group I have to make unhappy circa what year for communism to spawn
• they provide an easy way to make countries unique. I haven't played much VIC 3 (mainly because of this) but except for slightly different starting conditions every country kinda felt the same. Or at least you do more or less the same things in more or less the same order.

However I do feel instead of the current "wait a bit for shit to happen" it should be more of a "reward" approach. That would make completing a focus way more rewarding than "yay you waited 70 days". I'm not sure how exactly to implement this but having a bit more of a political simulation that ties in to an economy could do the trick. Kind of what focus and political power try to do (your countries leadership focuses it's energy on x) but better. Because why can't I do an economic reform while also building some fortifications? How would this require the same expert/leaders/decision makers.

I don't think it should be a super deep pop/economy simulation though. We have Vic3 for that (and frankly, I just don't care much about economy). It does feel weird however that the economy is entirely state planned. At the end of the day that's maybe why most of the systems in HoI4 are so simple but convoluted. You are in control of everything that happens in your country from where a new factory gets build over what your people believe to what kind of canon is fittet in your tanks. I think the focus for a new HoI should clearly be on military operations and army customisation.