Ah, you're right. Knights are certainly not equal to Rooks in this game. But they do gain value from their ability to jump, AND Betza's leveling effect. If all the pieces were equal in value it would be a dull game, where people would exchange pieces and reach a pawn endgame.
Incidentally, I think the bishop, on a semi-open position, is stronger than the Rook on this board.
This is a diagram for the Nightrider's movement. The squares marked with & are can be reached by more than one path.
+---+---+---+---+---+---+---+---+
8 | |:::| * |:::| & |:::| * |:::|
+---+---+---+---+---+---+---+---+
7 |:::| |:*:| |:::| |:*:| |
+---+---+---+---+---+---+---+---+
6 | & |:::| |:*:| |:*:| |:::|
+---+---+---+---+---+---+---+---+
5 |:::| |:*:| |:::| |:*:| |
+---+---+---+---+---+---+---+---+
4 | |:::| |:::| N |:::| |:::|
+---+---+---+---+---+---+---+---+
3 |:::| |:*:| |:::| |:*:| |
+---+---+---+---+---+---+---+---+
2 | & |:::| |:*:| |:*:| |:::|
+---+---+---+---+---+---+---+---+
1 |:::| |:*:| |:::| |:*:| |
+---+---+---+---+---+---+---+---+
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