No, they are entirely different features. Pointer authentication is largely a control-flow integrity feature. Hardware memory tagging attempts to prevents arbitrary overwrites/memory corruption, even to data. There are dozens of other features that prevent memory corruption and it's not really "playing word games" to distinguish between them.
I assume you're not talking about this: https://developer.apple.com/documentation/security/hardened_...? And to your other point: the difference between these things do matter because they have entirely different semantics and protect against different things, although the overarching goal of preventing undesired operation is the same. Taking the metaphor one level up to apply to computer science rather than security, this is like saying that the borrow checker and asserts are both the same from a certain point of view because they both help prevent bugs. Which is true, of course, but when you're talking about a programming language's safety features saying something like "C can prevent use-after-free because of its borrow checker" is not correct nor can you make it relevant by saying something like "yeah but C has asserts and they also help prevent bugs so from my point of view I think you're being pedantic".
Thing is, every time we discuss this it ends up following the same path.
I see these iOS features as a mechanism to improve C safety on iOS, while you don't.
We would be better if Apple would just reboot the whole stack in Swift, but that will take years, if ever, so from a security advocate point of view, I see that better as what PCs offer nowadays, specially after the misstep that MPX ended up being.
I have nothing against improving the safety of languages that have historically had issues in this regard; in fact, I have actually called out companies for turning off mitigations: https://news.ycombinator.com/item?id=23448161. The point I'm making here is that the things you mentioned are different things and they protect against different types of attacks.
Just for completeness, BTW, iOS devices after iPhone XS ship with PAC, which is part of ARM-v8.3; memory tagging is an extension of ARM-v8.5. Rumors point to the A14 chip supporting that but there's no word on whether Apple will support the extension.
