I think I understand both sides of the argument where some says Talia is good at manipulating turn meter and others say she has weak heal.
I think both are true, while which characters beats which characters in battle no long says anything about strength as it is possible that the weaker characters beat the stronger characters in battle if AI controls the stronger ones; however, does Talia need to be buffed in order to be competent? Yes.
I had Talia at 7* and gear 7. She does about 1100-1200 damage on her basic attack, which rarely critical hit, and her heal is about 4*40%-20%=140% team health; in contrast, luminara's basic attack does 1800-1900 damage, which critical hit half of the time at 3100-3500, along with her force push that does 5000+ critical damage often, and her heal heals team for 40%*5+20%*5+20%*5=400% team health.
From these basic data, talia is no where close to comparison with luminara.
In practical battle, we know how unequal numbers of characters at each side can turn the battle lopesided, yet i believe it is currently possible for 3 luminaras to beat 6 talia, while 3 talias hardly stand a chance against 6 luminaras.