Hey I was just making sure Seras has something to match Tsunade's Genesis Rebirth.(since its a fist fight she still gets it) To be honest, someone with a standard handgun could take out most of the Naruto verse since high-powered projectile weapons(non-jutsu) don't really exist in the Naruto verse and the energy projection that they do have is usually a high-powered mountain buster;this kind of make the bullet timing argument an unfair advantage over Tsunade.
And I'm not so sure Tsunade Flailing her arms around would really affect Seras unless Seras ran right into her range. Even then she would have enough time to make a death blow or something wouldn't she? Unless Tsunade has some great reaction time(she a ninja so shouldn't she?) Seras would end it but would have to run around during a good duration of the fight.