Miyuki could have froze them, it was self defense. Sh did it in volume 14 or is it that she was unable to because the Cast Jamming was too strong? It says she could only reduce the effects.
Bluestrider25 wrote: I would say that Minami is stronger than Izumi as well. Because everyone knows the Saegusa twins powers are at their highest when they are working in tandem.
The reason I would assume Tatsuya would send them back is becuase: A. he never wants to put Miyuki in harms way or in a potential negative spotlight. B. Izumi doesn't know his full capabities. Remember half of his abilities are considered top secret, so he can't fully release his strength with witnesses around if he can avoid it.
Also, while it may be ok to use magic to defend themselves from civilians (muggles), it would be a disaster if they used magic to fight back. Tatsuya pretty much doesn't care about getting introuble himself, but the biggest thing is he can use his physical abilities to disable most of them. So if the magicians defense magic is being eroded by Cast Jamming their only option would be to use offensive magic or runaway (if the magicans lack physical prowess). Most likely, the humanists want the outcome of offensive magic being used because even if they are hurt, pubiclly and politically they would still win the match and further their agenda against magicians.
Minami is stronger but the twins are not limited to a tandem, they are strong by themselves as well. In tandem they are much better because their special characteristics double the power of their attacks.