Although armor and auras can be similar, the brains required to use them are worlds apart. Zilan, Makindi auramancer Illustrated by Howard Lyon Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Legal Brawl Not Legal Legacy Legal Comp
The two piece Ultimate Guard Boulder Deck Box certainly earns its rock-based name too, feeling like an absolute brick when its filled with cards
However, with the basic Swamp requirement, your mana base needs to be almost exclusively basic Swamps and Cabal Stronghold to really make Cabal Stronghold function, which probably isn't worth the cost in Modern, where splashing a second color and playing utility lands likely give you more power than maybe making extra mana with Cabal Stronghold, and it might not even be worth the cost in Standard
Also doing heavy lifting with Kenrith: Biomancers Familiar is another Training Grounds that can actually attack too, but being a creature makes it much more vulnerable in a game of Commander than an enchantment which is why Training Grounds gets the #1 spot
