I think you've unfortunately got suckered in by Unity marketing wholesale, and things would stand to be cleared up a bit.

Unity's whole shtick is that they make something horrible, then improve upon it marginally. The ground reality is that these performance enhancement schemes still fall very much short of just doing the basic sensible thing - using CoreCLR for most code, and writing C++ for the truly perf critical parts.

IL2Cpp is a horror-kludge of generated code, that generates low-quality C++ code from .NET IL, relying on the opitmizing compiler to extract decent performance out of it.

You can check it out: https://unity.com/blog/engine-platform/il2cpp-internals-a-to...

The resulting code gives up every possible convenience of C# (compile speed, convenience, debuggability), while falling well short of even modern .NET on performance.

The Burst compiler/HPC# plays on every meme perpetuated by modern gamedev culture (structure-of-arrays, ECS), but performance wise, generally still falls short of competently, but naively written C++ or even sometimes .NET C#. (Though tbf, most naive CoreCLR C# code is like 70-80% the speed of hyper-optimized Burst)

These technologies needless to say, are entirely proprietary, and require you to architect your code entirely their paradigms, use proprietary non-free libraries that make it unusable outside unity, and other nasty side effects.

This whole snakeoil salesmanship is enabled by these cooked Unity benchmarks that always compare performance to the (very slow) baseline Mono, not modern C# or C++ compilers.

These are well-established facts, benchmarked time and time again, but Unity marketing somehow still manages to spread the narrative of their special sauce compilers somehow being technically superior.

But it seems the truth has been catching up to them, and even they realized they have to embrace CoreCLR - which is coming soonTM in Unity. I think it's going to be a fun conversation when people realize that their regular Unity code using CoreCLR runs just as fast or faster than the kludgey stuff they spent 3 times as much time writing, that Unity has been pushing for more than a decade as the future of the engine.