Those two are related in principle (the whole All Writs Act thing), which means in so far as you agree with Apple, but disagree with the hypothetical analogous gun manufacturer, maybe it's not so much the common principle (applying the All Writs Act) you take issue with. Which was your point, and it's a good one.

At the same time, it's hardly an unreasonable or inconsistent position to take. You can be opposed to the government asking Apple to install a backdoor regardless of constitutional concerns.