I too really love C#. That said, C# biggest weaknesses IMO are all around a lack of proper const-like markup. Given that TypeScript (another language by the same designer) exhibits similar weaknesses, I've always interpreted it as an intentional weakness introduced by the language designer.
Working in a fully const-correct codebase in C++ is a joy. Working in a partially const-correct codebase in C++ is a nightmare because everything has to work around the semantic expectations of everything else.
Anders Hejlsberg, and those who took over the C# language design after he moved on to TypeScript, were certainly aware of how to make the language fully constable. The fact that they didn't leads me to believe they viewed it as a trade off between how much benefit do you get from using it vs how much cost do you take on from having that markup need to be everywhere in your entire language ecosystem. It's not enough for one application architect to say they want to take it on. Every engineer working on every library and every potentially reused function would have to take it on, because constness done right either tendrils everywhere or is a lie, and there are big costs to extending those constipation tendrils, just as there are big costs to not having them.
Working in a fully const-correct codebase in C++ is a joy. Working in a partially const-correct codebase in C++ is a nightmare because everything has to work around the semantic expectations of everything else.
Anders Hejlsberg, and those who took over the C# language design after he moved on to TypeScript, were certainly aware of how to make the language fully constable. The fact that they didn't leads me to believe they viewed it as a trade off between how much benefit do you get from using it vs how much cost do you take on from having that markup need to be everywhere in your entire language ecosystem. It's not enough for one application architect to say they want to take it on. Every engineer working on every library and every potentially reused function would have to take it on, because constness done right either tendrils everywhere or is a lie, and there are big costs to extending those constipation tendrils, just as there are big costs to not having them.