Alright, I'm gonna be the sourpuss here. Chandra is not JTMS. The comparison is frankly laughable. That does NOT mean that she isn't a good planeswalker; in fact I would say she is likely the best chandra ever printed... but the comparisons to JTMS are overblown.
Just gonna put that out there.
Well, let's break it down. Jace's best ability is probably brainstorming every turn. Chandra's first +1 is probably comparable. She draws you a card. If you can't use that card, it turns into a free shock, which is indistinguishable from a card in a red deck. It's not the same level of card selection, to be sure, but the option for free repeatable damage every turn likely balances that out.
Jace was good at protecting himself with his -1. Chandra's -3 is better, since killing a creature is better than bouncing it. You can't do it as often, but killing a creature tends to be more permanent, so you won't have to do it as often.
Fatesealing ins't bad, but I think ramping by 2 is stronger. Consider that if you have a 2-drop in your hand, Chandra is effectively a 2 mana spell.
Their ultimates both win you the game very quickly, but Chandra's comes online faster.
Like, I don't think she's just equal to Jace. I'm saying she's
better than Jace.