I would not call tager slow IMO. Yes, you can do more charges but it is not like you can do it when ever you want. Tager has magnetism which makes him go faster and looks like it can do alot of DAMAGE if you are NOT playing safe. Also, he has got a projectile
vs Ragna, Tsubaki has a slight disadvantage because Ragna pretty much surpasses Tsubaki in every way. Damage, range, priority, invincibility, etc. However, Tsubaki's speed is greater than Ragna's speed. Also, most of her combos end with knocking the opponent far away from her into the corner so that you can do another combo. I don't know anything about bang yet. So i won't comment :P
Lastly, Tsubaki has got a good knockdown IMO. I don't think that she needs a bigger knockdown move.