When it comes to creatures, spells, and land, Wizards has years of experience and data to figure out what the right baseline power level is, and as we just talked about, they tend to aim far enough to the "safe" side that even if they miss, the result is a very good card (like Collected Company), rather than a ban-worthy monster
While three mana is certainly on the upper end of what's often playable in the card selection world, the power here is just too strong to ignore: digging five cards deep is an absurd amount of selection, and the difference between picking up one card and picking up two is huge
It will come at you fast with lots of flavor, but then pack a back-end flamethrower
They are great at one specific thing and do lots of other things passably well to offset the narrowness of their main perk
Beauty and the Beast dominates with 3 of the top 5 Floodborn cards
For example, just imagine paying 4 generic to Evoke Lamentation