No, they aren't.

I got 4th in a climbing race in loafers and Look Keo pedals a while back. If I had a brain and had remembered my shoes I might have won it. Sprinting was greatly compromised (though I still beat some guys), and climbing was no bucket of fun.

People pull out of pedals on the upstroke in sprints, you lose that power on platform pedals. When I do sprint and shorter distance events on the track I use clipless and toe straps. Huge amount of force generated there and even with the pedal adjusted to maximum resistance, I was still pulling out.