Agreed, Caravelle and DC 10s windows were well rounded! Still, it seems to me that the shape was more like a contributory factor rather than the initiator of the failures.
Early welded Liberty ships often cracked and split around their cargo hatches (sometimes completely bisecting the hull!) until these had their corners radiused, and I think this example has led many people to make a simplistic comparison between Liberty Ships problems and the Comet's (pointy-cornered!) square windows! However, the cause and effect was not the same in both instances : it was the whole design and build of the Comet's windows, skin, added rivet plates etc.which introduced the problems, rather than just the shape.