That doesnt even factor in cards like Gyre Sage and Marwyn, the Nurturer that double their power and thus mana production through this ability
Ripping your opponent's hand apart by forcing them to discard two cards feels great, but Junjis second ability to return a creature from any graveyard to the battlefield under your control is much more appealing
Instead of choosing between attacking you or casting things, they'll usually attack elsewhere and cast too
Erasing it is much cleaner but creates a ton of debris, eats through erasers, and uses lots of elbow grease
The transformed side being essentially a The Scarab God token is just the icing on the cake
I do think a lot of these cards need haste because you only have a single opportunity to swing with them and then they are gone, but maybe that final trigger is more than enough