Five years are about the edge for a desktop system. Both in the sense that it is doable since things are starting to fall apart but the technologies have not diverged too far yet and it may be still acceptable for conservative users.
Please go and read the actual conditions for RHEL. The later stages and extended support are clearly meant to just keep installed systems running. You get no new features, no support for newer hardware, services, file formats, etc. This is fine for a server that has a dedicated task to do. It is also fine for a single-purpose user machine, for instance used to control an instrument where you do not want, ideally, any changes at all (hence, little support). But this discussion started about desktop distros. And for a desktop (as in general purpose user system), not being able to connect most hardware newer than 10 years old, open any file formats that have appeared or changed substantially in last 10 years, use various services due to too ancient clients, ..., is deadly.
Also note you pay rather a lot for RHEL support -- fixing security holes in ten years old programs is terribly ungrateful work. Since community distros cannot make the contributors do it, those that tried to introduce this kind of long term support have all failed.