> UI isn't a strength on .NET to begin with

Sorry but remark only reveals lack of knowledge of what Forms, WPF and UWP are capable of, their related tooling and component libraries from the likes of Telerik, DevExpress, ComponentOne, among others.

Practically most modern Windows applications are mix of .NET and C++ libraries accessed via C++/CLI, P/Invoke or COM/UWP.

Plain old Win32 is left for legacy, games and a couple of unicorns like Adobe's Photoshop.

Application architecture design are the tools available in Visual Studio Enterprise for end-to-end application development, and modeling mapping into code modules, also known as Application Lifecyle Management.