Just look at the BPs, they shipped all of them with the dev tools so they are directly accessible to you, the “blueprints” are just subclasses of the base c++ class (item/creature) to set variables, there is literally no Blueprint scripting nodes in any of it except for the HUD (fine) and AI (using states). In fact I don’t think any of them know how to even use the blueprint scripting system based on the template mod they shipped out as it is an in efficient rats nest of nodes, so if anything they are lacking in knowledge with the very thing you accuse them of solely using, also please don’t say that blueprints are converted to c++ again.
You are showing a direct lack of understanding of UE4 by declaring any of this as a problem. You are totally correct that there is a blueprint for each item and creature in the game, they expose public variables to the designers to change values in, however there is NO game logic in any of them as that is all handled in c++. They are using the engine as it was meant to be used currently.
You can even directly use Stat Unit in game right now since it has console accessible and see that the game isn’t CPU limited at all, so even if they were doing what you claim, the problem STILL isn’t there, but would be with the rendering pipeline that they set up and their Global Illumination.