The balancing is indeed good in this game, no characters are broken or low tier besides Inferno. No, Tira is not low tier. You either can't see her strengths or you haven't fought any good Tira players, or both. And SCV is not a bad game, why do you act as if that game murdered your entire family?
She has some good tools, but she is a B tier character. Her punishment is quite good, but she has only one dangerous low (SPR FC 3KBB), her oki game isn't that good in neutral (only after combos) and she has one of the weaker Soul Charges in the game. She can do crazy damage with some of her lethal hits, but they involve hard reads/specific setups so they're not easy to do. Her standard combos do decent damage, but 22B+K scales heavily. One combo involving her C6BB+K after 22B+K only adds a few points of extra damage compared to the shorter combo that doesn't use up her spear stack even though it clearly looks like it's stronger. Also, her ring out game isn't that good, she was only ever a ring out queen in SCIV anyway. She just isn't as strong as some other characters.
Her B+K was always useful. It's not very unsafe, knocks down on hit, tech crouches, deals some good guard damage and can guard crush. The move is actually superior in SCV. In that game, it's almost impossible to block punish because it's only -10 and does a lot of pushback (only α Patroklos CE & Cervantes CE can punish it). The base damage is also slightly higher and it can clean hit. Yes, clean hits, those moves that can randomly do extra damage which isn't a mechanic in SCVI. Most characters can punish it in SCVI because it's -12 now and does less pushback. The only advantage it has in this game, is that they gave it a lethal hit property. That sounds good, but you can only do it after KO'ing someone with a CE so you won't be seeing it often.
I also like the changes to her charges. The timed versions in previous games are awkward and restrictive though I can understand if it upsets some players because it makes her a bit less difficult. I myself only started playing her in SCVI. And her design looks good in this game.