Rather than offering focus trees and technology slots that present 'no brainer' solutions to players. Having a set amount of leadership as a resource to allocate to technology, spying, diplomacy, and officership offers a much more engaging balance of needs to players. I also think the recruitment of units through the use of IC was a better trend than how it's done in HoI4. The only way HoI4 is better in this regard is that the production of specific equipment (and looting of it) has a much better degree of fidelity (rather than being a production slider).
I think the logistics model presented by HoI3 is a better representation of the challenges armies faced supplying their troops and managing their war resources. I think HoI3 is superior in the following ways:
