Ya, Frost Lich Jaina tends to be broken in Arena as a lot of strong cards are. She pairs so well with Mage’s elemental package and one of its best win conditions, which is Grand Finale.
Even when a Mage draft fails to provide a Grand Finale, it can often be discovered from cards like Runed Orb.
https://imgur.com/a/ie67zgb
https://imgur.com/a/qx1Yc82
Bloodreaver Gul’dan and Bru’kan of the Elements tend to be even more impactful hero cards in Arena.