Open Water vs. Flip turns

Which is harder? I figured flipturns are necessary for training to compensate for the continuous swimming in open water, especially in choppy conditions. But I finally came to the realization that I just can't handle it beyond about a mile as the cumulative effect of flipturns take a toll and leave me gasping for air. Yet I've done several one hour open water swims (about 2 miles for me) without problem. I don't know how much of this is because I am just relaxed without a pace clock.