In a corner you do not need full power from the engine so it's not really a surprise he was still competitive there, he suffered coming out of a corner though.
Not coming out of the corner but accelerating to the next one it helps. You cannot dismiss the levels of downforce the red bull showed. Yet as you say he suffered coming out the corner but his sector times where still up there despite the lack of power.
That to me says the Red Bull is by far the car to beat. Alonso turned some impressive laps in clean air but the Red Bull has serious qually pace, so getting that clean air will be so much harder.
Mind you it could all be up in the air if bridgestone change the compounds.