This is a situation where I’d say just make a ruling. If you think this effect was too powerful then speak to your players about it and adjust it until it feels right. This may require some trial and error but that’s the nature of a freeform magic system.
As far as what Ceremonies ‘should’ do, honestly that depends on which words are being used and how the players are interpreting them.
Bear in mind that the example you’ve given, the monster has below average hit dice for their HD and it sounds like the player is playing in a smart way. Also bear in mind that monsters can always run away, they don’t have to fight to the death every time.
Ultimately, use your best judgement and have fun with it. There aren’t any wrong answers.