I haven’t been seeing any Jaina’s lately, and the reasoning seem to be very obvious - because Tassadar was reworked into a mage, and he seem to be able to do everything that Jaina can do, but better.
Jaina has slows? Tassadar has slows as well. His Q slows everyone he touches for 2 seconds, and it’s a greater slow of 30%. On top of that, shock ray has a much longer range and can hit the backline whereas Jaina can’t. Tassadar’s autoattacks also slow, and at level 4 he gain endless shields per second. This is much sooner than Jaina’s level 13 ice barrier talent.
Tassadar also has better waveclear, and better camp clear than Jaina. Tassadar can clear a wave with just one W and Q, which costs FAR less mana than Jaina’s W and E. On top of that, Tassadar has baseline mana gain, far better than Jaina’s fingers of frost which requires collecting 20 globes and even after collecting, it doesn’t mana regen as much as Tassadar’s trait. And even worse, Jaina has to TRAIT into PvE (fingers of frost, Q pierce, and Q CDR), whereas Tassadar has excellent PvE starting level 1.
Ultimates? Tassadar’s ultimates are better. Water elemental? How about turning into an Archon and being a “water elemental” yourself slowing everyone around you? Black hole and ring of frost function differently, but black hole is much easier to land.
Both are immobile, but Tassadar is “less immobile”. He can shadow walk away from danger at level 13, and he can talent into movement speed at level 4 (not that it’s a good talent since it’s competing with an OP shield talent)
And this is not including the fact that Tassadar has force wall to secure kills, something that Jaina doesn’t have.
I think Jaina need some buffs, or at least, some rework in order for there to be a reason to pick Jaina over Tassadar.