Streamlining the game for The Me Generation for title sales, rather than taking the complexities of HOI3 and making them easier to perform.
Research in HOI3 was easy, you just need to understand the techs and their impacts. Production was easy, just form a division until you like the pros/cons, and click build. Grand Scale combat was easy, just assign units to a theater and turn on AI.
Now here are a few examples of what was difficult from HOI3:
1. Understanding the techs and impacts - I am not gonna buy this game if I have to read the forum everyday for 2 years, to understand the documentation - HOI documentation with all mechanics and explanations should be built into the game - having brief documentation, relying on 3rd party wikis and guides, and using the forums (which had answers, but took forever to find thm) with game registration as your form of software anti-piracy is done by a 3 person dev company working from a garage, not a software game company. If it has no documentation, it's not a finished product. There are some mods that had better documentation than HOI 2 and 3.
2. Clicking in production was easy, but what you do with those divisions after is the hard part. Breaking up divisions to reform new and better divisions to strategically counter your enemy takes FOREVER. Bulk operations need to be created...well, better ones. The GUI organization model was great for divisions in HOI3, but it needs to be broken down to brigade level. And make a method to perform same task multiple times. If I drop 5 Engineer brigades onto a Corps with 5 divisions, what should happen? 1 ENG is assigned to each divisions. Things like that. Keep the complexity, just reduce the fargin clicks needed to do it.
3. Grand scale combat requires use of the AI Control, which no good player EVER uses. I WANT TO USE AI FOR MY UNIT CONTROL! But it only works well if you have overwhelming odds. The problem is that the AI has flaws in land combat which were NEVER fixed, and it was terrible for air combat, and absolute garbage for naval. And much of that was to do with AI's lack of ability to assess the situation and make SMART changes.
These are just a few examples of the things that were bad in HOI3, and you don't correct a problem by removing the situation which causes the problem. You fix the bloody problem! Don't dumb this game down, just because you couldn't get things to work well or correctly in HOI3. That is the worst idea for HOI4.
