Re: Covered humbucker pot value
No, I would say that the two are not comparable.
The difference with a good quality (e.g. Seymour Duncan) humbucker cover vs. open coils is barely audible IME, if at all. OTOH, the difference between pot values can be very noticeable IME.
I loves me my treble (can always be reduced later, but can't easily be added later), but I have zero worries about covering a humbucker. If that's the look I want, then I put covers on, without thinking twice about what it will do to my tone.
All that being said, I would be using at least a 500K pot with a JB, and I actually find 1M better, myself. Those pickups really smear over and obscure the high end, inherently.