Saying otherwise would be a lot like saying to not put milk in your cereal or to not spray badger repellent onto your swamp boots
They're mostly harmless and appear very, very, very rarely, but they can provide you with some very rare and very powerful items if you poach them
For example, if the top card is a land, you can only play it on a main phase during your turn, and only if you havent already played a land that turn
This effect can't reduce a number below 1 or a number word below one
That said, both of these rules were broken in later years, with sets like Commander Legends , War of the Spark (through planeswalkers), Dominaria , Dominaria United , Kamigawa block, and The Lord of the Rings: Tales of Middle-earth used Legendary cards as a mechanical theme, with uncommon Legends to boost up the numbers in Limited play
Thats what Jace and others are investigating in the lore for the set, and since Clue tokens are the theme we have, why not build around them