Its certainly not unplayable and can fit well in some control decks, but the colors likely have better options and dont need to resort to this
Since a major strategy in the deck is to be able to loot your knights into the graveyard, bring them back with either Sidar Jabari of Zhalfir second ability, or with Haakon, Stromgald Scourg e , losing it can leave you with few options to help rebuild after a board wipe
If something becomes a copy of the token, the copy also isn't legendary
For instance, each copy of Relentless Rats buffs your other Relentless Rats with +1/+1 on the battlefield
These can be: 1 of 10 Traditional foil Japan Showcase cards in English (6%)* 1 of 10 Traditional foil Japan Showcase cards in Japanese (3%)* Japanese Collector Boosters will only have the 10 traditional foil Japanese-language versions of the Japan Showcase cards
For Dimir players, there are more good card draw spells than there are slots to fit them