Park only did the surgery because he wanted to prove himself and had a score to settle by completing the surgery.
He hides it before he leaves to treat an emergency patient and even during treatment, because In-beom is a fellow General Surgeon, the two end up working on the same patient and the tension is palpable between the two.
I felt like the whole series picked up at about ep 7-8 and got really good from ep 9 on.