C++ is one of the lowest level programming languages to use, which is why it’s great for software development. When people say it’s faster they mean that it’s capable of getting more out of the hardware than by other methods. Blueprints to my knowledge has an insane amount of overhead. C# has limitations that C++ doesn’t. There’s a reason why most software development is done in stuff like Python and C++ (to my knowledge anyway). Parts of software code are even programmed in assembly which is the lowest you can technically go. There’s machine code but I don’t think that it’s very platform-friendly.
UE4’s priority is greater visual potential over simplicity and low overhead. There is a lot to improve on the performance side but in terms of features UE4 is right up there. I think by next year UE4 will be very solid.