It really boils down to what the board looks like. If the board is a regular 4x4, then Man is more valuable than Rook. Another example: in Mini Forest, Bishop and Queen wouls both be worth 5.
How do we know the value of a fairy chess piece

It really boils down to what the board looks like. If the board is a regular 4x4, then Man is more valuable than Rook. Another example: in Mini Forest, Bishop and Queen wouls both be worth 5.
not only the board, the entire variant and its rules also matters

Wazir is more powerful than Ferz. And on a less expansive chessboard, it also seems to be better than Alfil and Dabbaba.

Wazir is more powerful than Ferz. And on a less expansive chessboard, it also seems to be better than Alfil and Dabbaba.
True. the Ferz is colourbound, the Dabbaba is double colourbound and the Alfil is triple Colourbound

Mann/NRK is a bit better than the Knight. Take my rating as a proof.
How? Show me examples, I can show you examples of how the Knight is better than the Mann

The Knight is better than the Amazon
“💀” ahh opinion
but seriously: I know the knight is better than a non-royal king, but I am sane enough to also know that a Amazon is better than a Knight, a Amazon can do everything a Knight can do and everything a Queen can do

If you guys can handle the math, a full description of how to do it for any piece on any size board is here:
https://triceschess.com/articles_01.shtml
The value of a fairy chess piece is subjective yet objective
I don’t know how do we know how much a fairy chess piece is worth?
in my opinion the Rook, Wildebeest and General are all worth the same (5 points) but most people say the general is worth 6 points and I even saw some people saying it’s worth 6.75 (only 2.25 less than a Queen!), and someone told me the Wildebeest is worth 5.5 points (I know it’s only 0.5 point more than a Rook but I don’t know why people always underestimate the Rook infinitely long sliding moves)
I also don’t know why the Non-royal King aka Mann/guard is worth the same as a Knight, in my opinion the Non-royal King is worth 2.75 at its peak during end-games
I seriously don’t know how we know the value of fairy chess pieces, when I give a value to a fairy chess piece I always use my scale:
Knight: 3
Bishop: 3
Queen: 9
Rook: 5
Non-Royal King: 2.75
Alibaba: 2
Alfil: 1
Dabbaba: 1
Camel: 2
Wazir: 1
Ferz: 1
and many more…
the Answer is: I don’t know.