Yes it does "hurt" because it creates an inconsistent visual style. Windows is a mess because of the refusal to deprecate old APIs.

Windows is the practical behemoth that it is /because/ of Microsoft's refusal to leave old programs to rot. We use Windows so we can run the programs we want, and Microsoft will apparently move the Earth itself to make that happen.

I don't think moricons.dll is actively used by Window itself anywhere? It's a resource DLL you can reference to use icons from in your own program shortcuts and similar. It doesn't provide an API as such. It's more like a collection of known graphics files being shipped as part of Windows.

Sounds like a bigger attack surface for malicious actors.

Processes with write access to moricons.dll are able to do much worse things.