It depends, I've some some beasts built in ASP.Net Webforms. Worse than anything you'd see in PHP from a reliability and extensibility perspective (although factors better in security - Microsoft pushed their kludgy ORM hard back then whilst PHP tutorials started with string-based SQL).
If I inherited an ASP.Net Webforms product which was built by amateurs from an MVP/PoC which would go on to form a very small part of a large product then I would absolutely re-architecture (and thus rewrite) it.
If it's an existing product the the rewrite cannot be compartmentalized then there's no way I'd touch the code.
In the scenario of an aging product I think that you're honestly better taking your best engineers and product people and starting again. At some point when the new product is mature enough you can look at how to move the last straggling customers over. I've seen that done successfully by clients and also by large companies (Microsoft with WebForms > MVC and later .Net Framework > .Net Core).
WebForms is pretty similar to Coldfusion. Which he spent the whole start of the article saying was fine and got the job done.
There's nothing inherent in .NET that would 'not provide the type of experience that was best for this environment'. If anything, probably the vast majority of code that is written for managing 401Ks out there is probably written in .NET or Java.
If I inherited an ASP.Net Webforms product which was built by amateurs from an MVP/PoC which would go on to form a very small part of a large product then I would absolutely re-architecture (and thus rewrite) it.
If it's an existing product the the rewrite cannot be compartmentalized then there's no way I'd touch the code.
In the scenario of an aging product I think that you're honestly better taking your best engineers and product people and starting again. At some point when the new product is mature enough you can look at how to move the last straggling customers over. I've seen that done successfully by clients and also by large companies (Microsoft with WebForms > MVC and later .Net Framework > .Net Core).