No it's not. It performs as expected given the materials it is made of. The newer models are made of better materials but that doesn't make the iPhone 6 defective.
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The newer models are better. That's how it typically works, hence the common advertising slogan "new and improved". If you want a better phone, you have to trade up to a newer model.
Cell phones don't last forever. If you think they should last longer than 1 year, then vote with your wallet and only buy cell phones that have manufacturer's warranties of at least 2 years. Oh wait . . . . . there are none.