Using sickness as a loose point to my claim as that factor affects a team more by how much their opponents allow them, this split feels like a meta in which C9 is struggling to thrive in. Roster changes or not, there do exist some teams that look immaculate in one game style but not in another; MVP in the LCK being a direct (and worse off) counterpart.
Only pulling the games pre RR due to said sickness from the start, yeah C9 has been exposed more being inferior to the competitive meta and what kind of team fight and execution based capabilities are needed. Role for role, minus mid lane, there just exists better team synergy in other teams such as CLG and especially NV as two teams.
Long story short, I just think they lack mechanics towards team fighting this summer, and as such they're kind of running games without an identity.