> however, while I think that the SPA approach can be nice to keep the front end separate from whatever technology you use on the back end, it comes at a cost of duplicating your data model and the interfaces between them

Can you elaborate on this? I'm not sure I get it, because once you have your view model in asp.net, it seems like it should be easy to derive a JS/TS model from it using various techniques (reflection, source generators, etc.).