I can tell you're drinking. "The only difference is mana, so what." Really? REALLY? Tamiyo allows the opponent to continue to advance their board, while of Jace bounces a 5 drop, and they are forced to replay it, that's a Time Walk. I can't believe you don't see that. I feel her +1 is really good.. if you have a board. How many times have you guys bashed cards that require creatures to do things.. like Prey Upon, Valor in Akros, Retreat to Valakut, etc. (this list is near infinite). Without a board.. her +1 does absolutely nothing. The -2 is a wash.. as they are both powerful in the decks that they belong (Jace in control, Tamiyo in tempo).. but I feel her ultimate is WAY better than Jace's.. like, it's not even close.
You're too control minded with this post. For one thing tamiyo can use her plus on their creatures, which depending on the situation can shut them down entirely. But even if that weren't the case, her minus is as good or better if it's about protecting tamiyo herself, which is what I want out of a PW: The ability to cast her t4 and know she'll still be there when I start setting myself up to defend her properly. Why is Jace bouncing a 5 drop in the first place, I'm playing Tamiyo t4 ideally. Why not bounce Ulamog if we're going to exaggerate? Also, I don't care if she can bounce any of those cards... What if the 5 drop is an actual good card, like reality smasher... What did the bounce do then? Nothing at all. Or maybe it's Avacyn, or some other card that's actually worth playing in a competitive build.
I'm either playing her in an aggressive deck, and then her plus draws me 2 cards or better, or I'm playing her in a control deck and her minus buys me all the time I need.
Is she better than Jace? I don't know, I haven't even had a chance to try her yet, but I'm pretty sure she is.
P.s.: I can't believe you just tried to compare Tamiyo to Valor or Retreat.