It was not trivial but the subjective experience matters a lot. In migrations that I participated in the most difficult parts were not related to ASP.NET but to

It was not trivial but the subjective experience matters a lot. In migrations that I participated in the most difficult parts were not related to ASP.NET but to third-party libraries. Another pain point at the time was moving off WCF which ended up being packaged up on some legacy Windows host as a separate microservice for just that purpose to not hold everything else back but that's it. Swapping out the startup and hosting models was not a challenge because the APIs were comparable, some controller classes had no lines changed either, and moving off IIS pool arguably is all around improvement (and far easier, to manage with docker and deployment manifests).