So what? No one was trying to shield THEM, they were just trying to blast them. A link would be as useless as Cadsuane suggests when they are in the bubble-of-evil fog in the Cairhienin rebel camp. A sister is strong enough to kill people, so a link would take a dozen strong-enough guns and reduce them to a single overkill-gun. And some strength is lost in a link. The point is, linking offers no real advantage in a pitched battle, which is why the sisters did not even bother.

No, they didn't. They were holding six seperate shields (or one shield with six components) on him, otherwise, they would not have been able to tie off their portions. There would still have been one shield (one soft point), but it would have weakened as each sister was released from the link.

And they showed up rather late. The gradual departure of the sisters from Rand's shield shows that they were becoming increasingly pressed and in need of more help. Taim saved the Tower sisters more than he rescued Rand, since without his intervention, they would have been overrun. Once Rand broke out, all he had to do was Skim home, but he was pissed and looking for payback.

So they would still take the first hits. Their numbers would be reduced before they could ever strike back, and that is not good when you are facing a force that has superior numbers AND training.

UnSHIELDable, NOT unstoppable. Fireballs & lightning bolts don't do less damage just because they are hitting someone who is linked to another channeler!

And they would have no problem with that! Killing channelers is the next best thing to collaring them. If they cannot collar channelers, their priority is not "Let them live so we might harvest them another day" but "kill them, because the worst thing ever is a loose mareth'damane." The whole premise implicit in the notion that the inability to be shielded would be some sort of insurmountable advantage for the Aes Sedai, is that the Seanchan will ONLY try to shield them, and would not kill them. In fact, they would do so happily.