The situation was far from ideal - or at least that's how it appeared to be. Whether it was Lex himself, or Giselle, or the formation, all three were weak points. Whichever one of them the enemy neutralized, the result would be the same which was a failure of the plan to disrupt the storm.
If Lex fell, the shields protecting them would fail, thus destroying the formation and injuring Giselle. Heck, Lex didn't even need to fall, just suppressed to the point where maintaining the shield was impossible.
If the formation was destroyed, then their presence here was pointless. If Giselle fell, then Lex alone could not make the formation.
To make matters worse, only Giselle could defend against the enemies, because Lex was too overwhelmed just defending them. Of course, that's only how it appeared on the surface.
