If the hypothetical writer/producer of a pending TV series were to announce tomorrow that he'd locked down four seasons worth of narrative arc prior to having shot a frame of footage, I've no doubt many people would think "Great; that's certain to result in a really dramatically satisfying viewing experience!"
My reaction, on the other hand, would be "You're either lying, or you're an idiot, and in any case I have no interest in watching so rigidly pre-plotted a series."
Well, at this point, I agree with you that my reaction will be "You're lying." I accept a certain level of spontaneity, but I'm about done with "Great Big Mystery" shows. In my experience, they rarely satisfy IF you're watching for the mystery.
If you're watching to watch the characters just do whatever and be characters, you have a much better chance to enjoy the series -- whatever series that may be. But if you're watching to "solve" the big mystery, what are the odds that:
(A) the big mystery even HAS a solution in the writers' minds?
and
(B) the solution they have in mind doesn't suck? (IE: "Uhh...God did it! Oh, and it really WAS purgatory all along. Oh, and the truth is...umm...there was a government conspiracy about aliens and...uh...you can't stop it. Or something.")
AND
(C) the show won't get canceled two seasons into its planned six-season run, leaving the questions unanswered?
Based on my experience, at this point, I'd say...the odds are pretty ****ing slim.
As for the straw-man argument about "rigid plotting", who says you have to "rigidly" plot anything (unless any kind of plotting strikes you as rigid, I guess)? Have a starting point in mind, have an ending point in mind, and maybe have one or two high points in between in mind. Then fill in the blanks as you go. That's hardly rigid.
I guess I just don't buy the notion that you can't have a plan of some sort, generally stick to it, and still have interesting characters.
I think that's a cop-out.