They're not amazing in multiples, though, so you cant put 12 of these in your deck and call it a day, so mix them with shock lands and the like
One of the more exciting things for players in Eldraine is the return of powerful creature-type specific commanders, with Faeries being particularly well supported in the set
Rather, treasure was designed as a utility mechanic which could be plugged in to bolster existing decks in some unique ways
Ursine Monstrosity is kind of chaotic (and in some decks, you want that), but it fits into self-mill by caring about the card types in your graveyard
Their ability to produce mana should not be underestimated, as you dont normally get such a cheap Commander who can make so much mana (Rofellos is banned, after all)
In most cases, this can fully remove a creature, and doing that at instant speed is pretty nice