Those guild jobs and side tracking by Lanuvel made him gain experience and knowledge, he didn't knew he could just buy weakened slaves to kill so he can exp boots, not like the raw number of exp or even stat boost can help without actual experience he use now.
Just because you used a cheat on the character in a game, doesn't mean you will know everything.
Also, Lanuvel was hired to summon him, be angry at her boss. She isn't the main culprit.
Also, also, albeit Lanuvel questions mc actions, does fallow him blindly and would give her life away if necessary.
Don't think he thought things through...