I think the main problem with Chandra is that she is nigh useless vs Shops, Dredge, Survival, Humans and of only marginal value vs combo. The same could be said for JvP though Jace does pull his weight shrinking an attacker or blocking with the "flip trick" every now and then.
In a control shell vs other control decks, is she better than JvP? She can flash back a spell right away (if you have the mana to pay for it) and can flash back two spells in a row, which does seem back-breaking especially in the case of Time Walk in particular. Is it worth the more awkward casting cost and loss of JvP's utility? I'm not convinced.
(She also synergizes with other red Planeswalkers, but IMO if you already have an uncontested Planeswalker in play, boosting them with Chandra is win-more).