Dewalt is pretty good quality, there's no way you should have worn out five bits doing what you did. You were probably not pushing hard enough on the drill so the bit spun in the screw heads which can thrash a bit pretty fast, not to mention the screw heads. But don't blame yourself; pushing hard on a Phillips is difficult. They are better suited to electronics or drywall where you don't need to push. Next time, use a square bit which is what a Robertson is called in the US. There were patent difficulties since the Robertson was invented in Canada. You should be able to find square head screws these days since Americans are starting to catch on that they're better. They work far better than Phillips when you need to apply a little force to get the screws in, and the bit will hold a screw in it while you get what you're screwing into ready with your other hand. If your drill has a torque adjustment, use it, it can prevent overdriving and stripping.