There was limited cover between where Cole was and the gates, there was no way he would not get caught up in a fight. The good news was the whole area was well within his domain, however he had to be in the right position to cast his techniques.
If he doesn't time it right there would problems and some of the monsters won't be caught up in the attack. He also had to keep his domain restrained, using it at its full potential would make the attack weaker and alert other monsters to the commotion. He had to bring down as much of the shark monsters as possible. Then use that confusion to skip past them, he just had to use Erasure to get to the right spot on time.
