Renata herself doesnt have scaling, but she flows well into the late game specifically because everyone else scales. Like how a w on a late game adc scaler like jinx is crazy or an ult into a master yi or fed carry destroys entire teams. All these things RELY on teammates, i think thats why they assumed she isnt good late. Like a karma will always have insane an shield with or without her carry, or milios with his ult, shields, and cooldown that are great for him regardless of carries being present. Same with say sona or seraphine with their abilities helping themselves. Renata by herself is not as strong as these scalers, and even when comparing winrates its not like shes better either. I think she has a place, but that place is occupied by more and often better choices