Agro decks want more proactive things in the top of their curve and typically don't care at all about the life gain which devalues the best bit of Ajani
The loss of life Jerren causes isn't exactly optimal, but you can easily offset this downside for two mana, Jerren can provide a target Human with lifelink until the end of the turn
If youre short on lands, youll lose tempo when you cant pay the mana cost for your spells
For example, any enter-the-battlefield Venture trigger combined with an infinite blink combo can mean an immediate win, thanks to the Lost Mine of Phandelver's Dark Pool room
Those qualities make cards like these incredibly powerful engine elements for combo decks
But, generally speaking, a fair graveyard deck might be one that seeks to reanimate or recur creatures for value, and try and win the game through swinging those creatures in for combat damage