The problem with Pawns is that they are severely area bound, so that not all Pawns are equivalent, and some of these 'sub-types' cooperate better than others. Bishops in principle suffer from this too, but one seldomly has those on equal shades. (But still: good Bishop and bad Bishop.) So you cannot speak of THE Pawn value; depending on the Pawn constellation it might vary from 0.5 (doubled Rook Pawn), to 2.5 (7th-rank passer).
Kaufman already remarked that a Bishop appears to be better than a Knight when pitted against a Rook, which means it must have been weaker in some other piece combinations to arrive at an equal overall average. But I think common lore has it that Knights are particularly bad if you have Pawns on both wings, or in general, Pawns that are spread out. By requiring that the extra Pawns are connected passers you would more or less ensure that: there must be other Pawns, because in a pure KRKNPP end-game the Rook has no winning chances at all.
Rules involving a Bishop, like Q=R+B+P are always problematic, because it depends on the presence of the other Bishop to complete the pair. And also here the leveling effect starts to kick in, although to a lesser extent than with Q vs 3 minors. But add two Chancellors and Archbishops, and Q < R+B. (So really Q+C+A < C+A+R+B).
The problem with Pawns is that they are severely area bound, so that not all Pawns are equivalent, and some of these 'sub-types' cooperate better than others. Bishops in principle suffer from this too, but one seldomly has those on equal shades. (But still: good Bishop and bad Bishop.) So you cannot speak of THE Pawn value; depending on the Pawn constellation it might vary from 0.5 (doubled Rook Pawn), to 2.5 (7th-rank passer).
Kaufman already remarked that a Bishop appears to be better than a Knight when pitted against a Rook, which means it must have been weaker in some other piece combinations to arrive at an equal overall average. But I think common lore has it that Knights are particularly bad if you have Pawns on both wings, or in general, Pawns that are spread out. By requiring that the extra Pawns are connected passers you would more or less ensure that: there must be other Pawns, because in a pure KRKNPP end-game the Rook has no winning chances at all.
Rules involving a Bishop, like Q=R+B+P are always problematic, because it depends on the presence of the other Bishop to complete the pair. And also here the leveling effect starts to kick in, although to a lesser extent than with Q vs 3 minors. But add two Chancellors and Archbishops, and Q < R+B. (So really Q+C+A < C+A+R+B).