One of the biggest mistakes the writers made, was leaving Ji Dwi in isolation.

He didn’t form any bonds with the Hwarang members, and thus the expectation for them to all serve him without hesitation is just so unrealistic. 

If the writers wanted Hwarang to be Ji Dwi’s men - they should have created that bond. 

Ji Dwi should not have spent 19 episodes of no interaction with the Hwarang members.