I don't think you can even begin to resolve the question.
As just one example, consider the dual sport possibilities on Vancouver Island versus, say, Utah.
A road can get cut somewhere on the Island to access a drainage for logging - and be completely overgrown and impassable even by foot 20 years later. A trail on slick rock in Utah... that one will be around for a while.
I personally don't think I've ever even looked much at routing on recreational GPS units. Perhaps because with a geomatics degree, I pretty quickly realized all the pitfalls when the mapping routing would depend on wasn't dead nuts accurate. The mapping we get in the military isn't even up to that dependability standard, so why would I assume I could find that standard on mapping that cost me something like $100 from Garmin, made to please as many different types of users and types of GPS units as possible?
That isn't an argument for or against routing, just an observation that routing might work great in some areas where the geography and the quality of the mapping supports it, while in other areas, the geography and quality make routing more of a potential pitfall than anything else.
You can add another aspect. Regularly riding and exploring in your local area, where you're regularly going "aha!" as you find yet another backroad that connects two or more other backroads you ride is far different than travelling a couple of thousand miles on some fixed holiday time to do a dual sport ride you've been dreaming of and planning for a couple of years.
Moral of the story is that whatever works for you and the situation at hand.