Hmm. Again, disagree. I returned the iPhone 6 a day after buying it because it was so light (compared to the 5), it almost blew out of my hand (well, the lightness plus the curved edges made it so easy to drop). Light phones are easy to drop because they reduce the sensory feedback you get from holding it. Are you saying that a couple of extra ounces can make a phone too heavy for you to hold without dropping? 🧐Disagree. I almost never drop phones regardless of if the sides are flat or rounded.
The thing for me that increased my chances of dropping a phone is its weight: the heavier a phone is the harder it is to not drop it.