While that cost might seem steep, its the centerpiece of the Natures Rhythm and Mono-Green Landfall decks that have taken over the Arena ladder
It just deals out the damage
The other option is to take advantage of the direct damage, which is good in its own right to either finish off a damaged character or get them within range to be banished but also works with the likes of cards that benefit from being damaged - such as Scroop, Backstabber - that benefit from healing damage, like Rapunzel, Gifted Artist, or from damage being dealt: like Beast, Relentless.
Grolnok, the Omnivore Magic has enough cards and mechanics that work from the graveyard to make self-milling a reward unto itself but I wont object to a mill engine that throws in something extra to sweeten the deal
But to add to this, its a powerful commander card that is featured in 70,000 decks on EDHREC.com and sees significant Legacy play to boot
cards with stronger nostalgia value pushed toward the higher end