Not quite. That's only true because playing conditions favor seamers over spinners more often than not. If cricket was only played on turners in the subcontinent, you'd be inclined to say that spinners are just plain superior to seamers. Yes, to an extent you're right that seamers are less reliant on the conditions and thus are generally the superior option but it's not quite as simple as that. Probability comes into it so I'd definitely go for 3-1 over 4-0. Thoughts?
Exactly - these days there are not enough spin-friendly conditions to make spin a viable option most of the time. In the days of uncovered wickets, such conditions were far more widespread and the best spinners were often every bit as good as the best seamers. That's not true any more, however.
That said, if I had the choice to put Anil Kumble or Bishen Bedi or Eripalli Prasanna into an attack to replace one of Waqar Younis, Anderson Roberts, Wesley Winfield Hall and Brian Statham - or Courtney Walsh, Ian Bishop, Jason Gillespie and Ian Botham - (and I've deliberately not picked any of those I rate as the very, very best seamers, I've gone for some merely-excellent ones) on a spin-friendly pitch there's no way I'd even remotely consider doing so. Even merely-excellent seam-bowlers are miles ahead of merely-excellent spinners.
You'd have to get into a situation of a spin-friendly pitch
and some merely-very-good seamers (such as Angus Fraser, Terry Alderman or Garth McKenzie) for me to consider even a top-of-the-general-standard-tree spinner (ie, not Grimmett, Warne etc.) being added in.
My seam > spin theorem only applies, it must be stressed, to the era of covered wickets.