If you see the onboard pole from last year, you will realize that, turn 4, 11 and 14 are not slow. They are more downforce dependent than mechanical. So, Mercedes wouldn't be struggling over there. It's only turn 1 (80 kph), 2 (82 kph), 9 (79 kph) and 15 (81 kph) that require more mechanical grip that would be crucial for traction from lower speed.
Most importantly, the tyres are not UltraSoft which is also another factor that would move the balance towards Mercedes.
The battle would be between efficient downforce and draggy downforce. Who have better co-efficient of Drag Vs Downforce. PU power isn't going to be overtly necessary, which means, Ferrari shouldn't feel left behind. But the question is, are they going to bring a new PU, which would have to conform to the reduced oil burning regulation. If so, how would that affect them?