This was a mistake on the part of the first prince faction.
If the attack was repeated two or three more times, the probability of Ariel dying would likely be very high.
If her servants hadn't been risking their lives to protect the princess, it could not be expected that Sylphy alone would be able to manage that duty.
However, the first call of the prince's lack of judgement on this matter, was no doubt owing to the combat prowess of Sylphy.