Kalista does not fulfill the expectations set by her storyline

"I invoke thee, Lady of Vengeance," she said, her voice low, trembling with the depth of her fury. "From beyond the veil, hear my plea. Come forth. Let justice be done."

Supports are typically nice guys and gals. The only mean support is Thresh and even he is there to collect souls. Adcs are the hotshot solo superstars. This is the way it is because champions typically look and feel like the way they play, and when an adc arrives on the scene, everyone bows to them and peels for them. Every adc has a little bit of Draven in them.

So we are asked to believe that Nami hates someone so much that she wants to summon Kalista and watch her kill them for her while she buffs Kalista? Um, no.

Do these look like the faces of hatred?

It makes far more sense the other way round: Kalista-as-a-support is summoned by, say, Graves still angry about the slammer, or Ashe who wants Lissandra and pig gone from the Freljord even at the cost of her own soul. Said Kalista-as-a-support then disables the opponent and watches with a smile on her face as Graves tells TF he won't put him behind bars and blasts his head off.

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In short, Kalista's lore portrays her as an enabler, but she actually plays like a selfish jet pilot adc bonding with people against their will and tossing them at the enemy to die for her. There is nothing wrong with this (aside from the grief potential, but that's on CertainlyT) if she was actually out for her own vengeance and used other people as tools to achieve it.

As is... she's awkward.