Yes. And the designers put that rule there for a reason. They actually expected it to do something, whether you like it or not.
They probably expected it to prevent druids from wearing metal armor, you know, like it says. If they expected it to prevent them from wearing medium armors, then they would have done it differently.
This is not how rules work! "It doesn't say I cannot change the rule so I totally can!" No, that is an absurd standard.
If there is no rule, what am I changing?
|Half plate||750 gp||15 + Dex modifier (max 2)||-||Disadvantage||40 lb.|
Those are all the rules for half-plate right there. If I put this on a character, I have changed nothing. If the designers didn't want me to make half-plate out of an alternative material (something that people have been doing for 40 years in DnD) and put it on my druid, then instead of "non-metal medium armor" they would have given druids proficiency in Hide, wouldn't they?
There is very good reason think it would alter the stats, because different material are actually different! There is a reason why armour that is said to be made of leather provides a lower AC than one that is said to be made of metal plates.
And the game certainly recognises this elsewhere:
And there is a very good reason to think it wouldn't. It doesn't. Nowhere in the rules does it say that if you make an item out of a different material that the stats change.
Also, interesting chart. It is meant for the destruction of items in the world, give you a rough outline. But, I can also tell you with 100% certainty and accuracy that it doesn't apply to armors.
Because Mithral and Adamantine Breastplates still provide 14 + Dex modifier (max 2) AC, they do not provide an AC of 21 or 23, the listed ACs for those materials. In fact, Adamantine armor and Mithral armor provide zero bonus to AC at all. Proving that armors made of different materials keep the same stats (though in this case they do provide specific bonuses based on incredibly special materials)
The rules do not specify the material of those objects. Thus it for the GM to decide what material is appropriate. Armours however specify their material, almost like the designers thought it would matter.
It specifies steel hooks in fishing tackle. Does that matter? Steel ball bearings, does that matter? The Xanathar's rules say that a Thieve's Tool Kit includes a small mirror on a metal handle, they specified that, so clearly that matters right? And if a rogue said that they pulled out a small mirror on a wooden handle, they'd be breaking the rules of the game and you'd give them this whole spiel right?
Because, you are really looking at only two options here. Either every single example I can come up with matters and was specified for a purpose that is ingrained in the rules... or none of these actually matter, and you are wrong about the armors. That's it. Those are the options here.
Either you say that every single herbalism kit every druid carries must contain glass jars or you say that the exact material of those jars doesn't matter and they could be ceramic or something else. Every single brewer must use hops to make alcohol, and they cannot make it without, because hops are part of every single brewer's kit, and that is supposed to matter. And on and on and on.
Your "it doesn't say I can't" stance is untenable. Rules do not work like that. Designers do not put rules that they expect to do nothing in the game. Complete noobs have no difficulty in getting this. They look the druid rule, they look the equipment description and pick a non-metal armour. This is how it is intended to work and Crawford's list of druid armours confirms this. You're literally arguing against the stated intent of the designer of the game.
No, I am not. Because the stated intent of the game is "non-metal medium armor". If they wanted that to mean "hide armor" they would have said "hide armor". Heck, Dragonscale is a magical item that isn't supposed to be considered in the balance. And they could have trivially made an exception for it in the rules for dragonscale, just like they did with Elven Chain.
They clearly intended for non-metal medium armors to exist, otherwise, they wrote a rule in the literal worst way possible.
People figured out 40 years ago that you could make half-plate out of things other than metal. Armors in the real world, like samurai plate were made from non-metal materials hundreds of years ago. Why is it so difficult for you to accept that they clearly intended non-metal medium armors to be an option? It is literally written in the book.