Look there are 2 types of ideas:I don't understand why so many people urge to revert most of new mechanism in HOI4. Indeed there are many bad designs in HOI4. However, many features in HOI4 are well-designed but ill-implemented. Those features shouldn't be thrown out of the window and revert to old system in HOI2, instead we should figure out some way to fix them. Like battle planner, if its AI is fixed I believe most of players will never want to go back to HOI2 where you have to micro every units. There are also some good design receive negative review especially the decision of removing money from the game. People propose adding money back to HOI4 every month on this forum but many of them just adding unnecessary complexity.
1) good ideas from the start
2) bad ideas good/badly implemented, which even if they work badly must be removed.
Most of Hoi4's ideas are of type 2. Because? Because, I quote an old school friend of mine "great ideas on paper, they are horrible once made real" which is EXACTLY what happened on Hoi4. The idea of the peace system, of taking away money, on paper are beautiful, but, as also said by the Devs, many ideas they have put in, HATE them! (peace system first of all!). Hoi3's peace system was ugly, but at least it avoided you bordergore.
The hoi2 system, like pace, was fantastic! Ditto the search system ... maybe the only thing that didn't work very well in the old hoi were the puppets. Here is Hoi4's tiered system I really liked for puppets. And I would like it back in a Hoi5. But for 1 nice thing about Hoi4, there are at least 2/3 things to throw in this game!
PS: the adaptive mission are a old feature of Eu4