Every Paradox game has its own specialization. From the diplomacy and economy of Victoria games to the pure combat of Hearts of Iron. Now that combat is getting and update, with a better AI.
During the development of La Resistance, work was begun on adding additional tools through an imgui that allow modders and users to see various internal data. In NSB, a significant amount of time was spent adding to this tooling and providing support for future AI development, as well as laying the groundwork for easier iteration on AI behavior and more.
While much of the work done here was an investment for the future, developers have also made some pretty big changes to the way the AI evaluates where it commits its troops and more.
The AI for assigning armor and special forces to appropriate fronts has received some improvement. The practical upshot of this means you ought to see fewer armor divisions assigned to inappropriate orders, such as garrisons, pure defensive lines, etc, and mountaineers used in frontlines that have the right terrain types.
And combined with the new supply system, the AI evaluation of where to put units has been totally overhauled. In practical terms, this is likely to manifest as seeing the AI commit more troops to defend key areas, such as ports & coasts, care more about the active supply situation on frontlines, and provide something slightly resembling a defense, in-depth for their own core territory, even during active frontline pushes elsewhere.
The AI was also changed in other areas, such as counters and naval invasions, which are quite similar to what we mentioned above, and will certainly bring about more interesting gameplay.