> It's diffeq solvers will almost certainly be worse than Julia (Julia is SOTA there)

Worse in what sense? Speed? Almost certainly not, since you would be implementing the solution directly in C++, so it will be as fast as you need(since you can use inline ASM). In Julia the really good diffeq libraries are not built in and this is not a diffeq solving library, so you would have to implement them yourself if you were just using this(so you can use almost exactly the same algorithms, and with more control over memory management in C++ you can maybe have it be a bit faster).