Definitly, that is the biggest selling point for Unity, it is a C# based game engine, with a C++ core like most engines, however what everyone writes is C#, with Burst (a C# subset for C++ like programming) they were even in the process of rewriting parts of the C++ core in C#.
So any engine whose game code isn't C# is a deal break for existing Unity users, as the only thing remaining are the assets.
