Who decided these magic item rarities?!

[Nytemare3701]

5e has a really bad habit of slinging content like a bad splatbook when it comes to magic items.

Seriously, the rarities make no sense, and aren't even appropriate relative to EACH OTHER, much less within the overall game rules.

Take for example the uncommon Cap of Waterbreathing. As an action, it puts a bubble of air around your head.
Then for comparison, the ALSO uncommon Cloak of the Manta Ray. As an action, you can breathe normally underwater, no bubble required...oh and it also grants 60ft swim speed.

Someone was nice enough to make a pdf with more sane rarities here.

[TC X0 Lt 0X]

Sounds like pretty typical 3.x magic item disparity made its way over. Im not at all experienced with 5e, but still these items seem of nominal significance unless you are going to have an adventure underwater. Are there any magic items that have a mechanical impact that isnt niche that are above the typical power of their rarity?

The cape of water breathing might actually have better use outside the water, kind of like a 3.5 necklace of adaptation. Sure the sim speed is nice, but blocking gases and other such things seems like a good trade off.

[Nytemare3701]

The pdf has examples, such as consumables costing the same as permanent items.

[Nunkuruji]

Usually gaps like that have a difference of requires attunement or not, or whether the slot has strong contention with other relatively strong items.

I took an initial review pass of them, big didn't dig too deep.

But yeah, seems like another thing they leave on the DMs shoulders.

[Agita]

I can't read the writers' minds or anything, but just judging from game design principles, I'm pretty sure the relative rarity of those two examples specifically has nothing whatsoever to do with the balance of their features or convenience. Neither one requires attunement, both let you breathe water indefinitely as a standard action, one also gives you a swim speed while the other makes you swim normally. That difference is practically trivial.

One is clearly better than the other, yes, but from a standpoint of what they do in the game, they both accomplish the exact same thing: They let PCs explore places that would otherwise be cut off to them. For the game designer, and for the GM, that one feature is vastly more significant than the swim speed. So what if one is strictly better than the other? It's the GM who decides what you get, anyway, or that's the default assumption. (Arguably, this means the two are redundant and one probably shouldn't exist. Sure. Also arguably, the difference exists so that the GM can decide whether they want to give their PCs the slightly more down to earth or "gritty" cap that only lets you breathe or the flashier and more convenient cloak. Matter of preference here, though it also serves the function of pointing out that there's not just one way to do a given thing and GMs can make up their own magic items even if there's already something similar in the DMG.)

Actually, if we realize that the two do the same thing, we can also figure out why they're specifically uncommon, and not rare or common or very rare or legendary. If you look on page 135 of the DMG, it recommends certain guidelines for access to magic items, and says that uncommon items are appropriate starting at level 1 while rare ones are better for level 5 and up. Now, Water Breathing is a third-level spell, so that your wizard will have access to it starting at level 5, if needed. So after 5th level, giving a cap of water breathing or cloak of the manta ray as treasure is less significant, because if the PCs really want to get past some water, they probably have access to a way to do that anyway. So levels 1-4 are when these items are both at their most interesting and exciting (but they're not common because that would say things about the game world you don't want to say about every D&D game world).