Exactly this. My current project is on full .NET Framework 4.8. It is on the latest possible version of ASP MVC, Entity Framework and all typical 3rd party libraries(of which 90% is supported on .NET 5). In the last two years we created several POCs for migration to .NET 5. Our current best estimate is 7 years for 80% of our development team. No sane manager will ever approve that crazy effort with almost no benefits for end users. Additionally we are talking here about most typical CRUD application without almost any advanced engineering. Our onboarding is taking at most 2 days and people can start be very productive even in first couple days. I can only imagine nightmares with more complex systems.