Some of the penances are just far too tedious to be done without either using an exploit or just being very lucky. You can play hundreds of matches with the same veteran and still never get those troublesome penances done. for example, for the veteran one of them require you to use all your ammo up and have 90% accuracy. another is completing a mission on malice or harder without ever being hit with a melee weapon.
these are some extremely unfun things to try and go for so why not give us a pity system to make it easier since the penances themselves dont even require skill to complete, just dumb luck.
my suggestion is that after a certain amount of matches played with that class the penance cosmetics are just moved over to the cosmetic store to be bought with earnable currency (probably priced at 500k-750k). or another suggestion is that for every 50 matches played the challenge becomes slightly easier until it finally just gets moved to the cosmetic store.