I have 2 theories atm:
Either they are jobbers and imu only needed them for their army and supply lines, given the framing of 20 kings vs the ancient kingdom involves more than a singulare fight, its like the raid on onigashima with the fodder samurai but bigger
OR they were all strong and imu tricked them, like with a contract or a loophole, and thats why he is so strong and he tricked them with a contract sapping their powers, thats why the stuff he gives out now are also "contracts"
I find the second one more intressting