There are certainly downsides here, most notably that exiling your fallen creatures eats into your reanimation options
I think I have one Avon Plains from back in the day but I have a hard time paying that much for basic land these days
Because of this, cube designers dont have to adhere to rules that are required for building decks for sanctioned Magic like Standard or Modern
Its an excellent glue card for many strategies: a good target for Birthing Pod, high-toughness, untapping is pseudo-vigilance, ramp, discard for graveyard value/reanimate, blink, the list goes on
While the deck looks super fun to play and Kalamax, the Stormsire is a potentially powerful commander, the precon doesn't go far enough to harness its power