Not indestructible at all--I run a repair shop, and 6/6+ are the most common phones we repair. The bigger the screen, the easier it is to break, in general.
You may have gotten lucky, or you may have a good case on it (a good case and a glass screen protector do go a long way.) But we've had people bring in phones even in very high-end Lifeproof cases with broken screens, bent frames, etc. It happens a lot.
Apple launched this phone because of the huge number of iPhone 5/5S users who didn't want to upgrade because they felt that the 6/6S was "too big." There was a fairly large/high-demand secondary market for 5S phones for this reason. Apple's hoping to pick up some of that market with the new SE.
The reason the 6 breaks so easily is because it can really easily fall directly on the glass. There is a little thin hard rim around the glass on every other iphone, whereas the 6 glass wraps around the side.
You may have gotten lucky, or you may have a good case on it (a good case and a glass screen protector do go a long way.) But we've had people bring in phones even in very high-end Lifeproof cases with broken screens, bent frames, etc. It happens a lot.
Apple launched this phone because of the huge number of iPhone 5/5S users who didn't want to upgrade because they felt that the 6/6S was "too big." There was a fairly large/high-demand secondary market for 5S phones for this reason. Apple's hoping to pick up some of that market with the new SE.