If you're not familiar with the system, why are you insistent on changing it? And since you're new to the team, what's the rush to tell everyone their work is poor? What would be your reaction if you were in their place? How do you think your approach will play out in the long term?
Sorry that I present myself to be critical to the team, I am not and I am impressed with how much they achieved given the time frame. In fact, all of the team are in agreement on most of the issues, but I am not entirely sure what to prioritize and how to balance it with the regular feature work
Leadership is about people not code. Good luck.