Haven't fully digged into it, but firstly, the executable is tiny, source code seems sane, performance for average sized projects appears to be better than existing solutions, and also some interesting features such as viewing texture/image buffers within the debugger

x64dbg is primarily made for reverse engineering but RAD Debugger is made more for the context of game development. Those are two different usescase with different priorities. I would expect source code debugging and debug symbol related features much more prioritized in RAD debugger compared x64dbg. Even x64dbg own feature list calls it's PDB support as basic. RAD Debugger supports natvis (same format as used by VS for describing how to visualize more complex data structures), I don't think x64dbg supports that.

A more relevant question might be what RAD debugger offers or plans to offer compared to Visual Studio C++ debugger. Based on http://web.archive.org/web/20230923095510/http://www.radgame... seems like an important part of motivation was providing Visual Studio quality or better debugging experience for Linux and console targets and doing that with single tool.