Iron Sand Kaiju is only good when Misaka is fighting huge foes like in that video.
it’d be impractical against a human sized, highly mobile target. Hence why she doesn’t bother with it in fights like with Brunhild
Eh, the kaiju's speed is kinda irrelevant when Killua can't climb it to reach Misaka (given it's rapid vibrations give each particle of Misaka's iron sand the cutting quality of a chainsaw), the Kaiju can regenerate from attacks, and with a Kaiju sized railgun the sheer AOE makes it much more difficult to dodge. Especially with Misaka's radar giving her Killua's exact position and the fact that it's still a railgun meaning it's still plenty fast.
Though even if you exclude the Kaiju Misaka still has plenty of options.
Though she usually uses coin for her railguns, as you should know she mainly does that to limit the collateral damage. she can actually punch much larger objects for a more powerful railgun like here
.
She can also make wings from water vapor
. Can call down natural lightning. And to go into more detail about rampage dress, it boosts her already impressive reactions along with her physical speed in general allowing her to...
completely blindside a character who later reacted to her lightning attacks.
And with her mastery of electromagnetism she could completely manipulate Killua's electricity attacks, and equipment like his Yo-Yos. None of Killua's ranged moves are gonna work whereas Misaka won't have the same problem. His only option is to try to get close and pull off his assassination moves but with Misaka's radar she'll know his position no matter how he comes at her and have plenty of time to react with a counter or defense.