Could it be more productive to work independently after PhD? Picture the following scenario:
X finished his PhD. X is also quite rich and can support himself (as well as his research) independently.

What do you think about this:

Would X's time after the PhD be well spent if he would just work 'independently'? Would this make things more difficult for him if he ever wanted to move back to an institution?

Is it in a way, in this particular scenario, not actually a very good idea, to focus solely on research and not bother with teaching and all the administrative stuff? Wouldn't he be more productive? What would hold him back?

Note: I am assuming that X is in the Humanities, that is, he does not require a lab or anything &amp; has access to a academic library / or has his own etc.
In academia, he might have


more exposure to interesting ideas (especially cross-field pollination),
better access to students and colleagues to exchange and refine ideas with, 
as well as external pressure to be productive (which might be a good thing.) 


While administrative work has never inspired me to have an interesting idea, teaching and mentoring students certainly has.

It all depends on the context he's able to set up for himself as an independent researcher. If he works better in isolation, maybe he'd be better off. If he can afford to hire other researchers and create an interesting intellectual environment, that might help.