Since, as you note, the actual values vary wildly with the position, I don't see the sense in working out "exact" values. There will never be a position where they apply.
They're just meant as a tool for beginners, when they calculate a long series of exchanges, they can try to keep track of the "points" to see if they are suddenly 3 down or so at the end. No precision is needed.
At higher levels, you stop doing that and instead visualize what is left on the board, and who is better in that position.
Hello Chess.com team. The only noteworthy issue I can think of right now is the (mathematical) value of the pieces, even though I'm perfectly aware this is directly dependent on the situation, e.g. a rook will do much more for you in the endgame than does a bishop and therefore win the game. But I have seen in some chessbooks and at chess.com that the values of the pieces are described as pawn=1, knight=3, bishop=3, rook=5, queen=9, while the king is rated as infinite, even though he occupies the same amount of squares than does a knight. Bobby Fischer credited the bishop 3.25 points in his book 'Bobby Fischer Teaches Chess'.
All these estimates are wrong in my opinion. I always had a feeling that there is something that feels 'fischy' about it.
Now, the way I determine the value of the pieces regardless of the overall situation on the board on any given moment, is to choose one of the four most central squares on the board which would be d4,e4,d5, or e5 and count all the squares each piece can possibly occupy or control from that spot.
A pawn always controls 2 squares no matter where it stands. Of all the 64 squares on the field, that's 3.125%
A knight can jump to 8 squares, that's 12.5%. Same with the king, although he cannot reach as far as a knight.
A bishop has got 13 squares, that's 20.3125%
A rook manages 14 squares, that's 21.875%
The queen commands 27 squares which make 42.1875%!
So, with the pawn's 3.125% counting as 1 point, it follows through simple calculation that the knight is worth 4 (as is the king, theoretically), the bishop 6.5, the rook 7 and the queen 13.5.
I was wondering how did the other evaluations come about?
You know, I like things as precise as possible.
Good luck with the answer, Werner 'Chessonimo' Wilding