The equipment has a tag and there is a restriction on a class based on that tag. What you're trying to do would be like playing a halfling, who have restriction on heavy weapons, and just deciding that you can get a greatsword without the heavy tag but otherwise identical. You seem to think that the writers just put in rules that do nothing. I don't. And my reading is backed by Crawford correctly identifying the armours druids are expected to wear under the rules; no half-plate included.
Tag? What tag?
|Armor Name||Cost||Armor Class (AC)||Strength||Stealth||Weight|
|Hide||10 gp||12 + Dex modifier (max 2)||-||-||12 lb.|
|Chain shirt||50 gp||13 + Dex modifier (max 2)||-||-||20 lb.|
|Scale mail||50 gp||14 + Dex modifier (max 2)||-||Disadvantage||45 lb.|
|Breastplate||400 gp||14 + Dex modifier (max 2)||-||-||20 lb.|
|Half plate||750 gp||15 + Dex modifier (max 2)||-||Disadvantage||40 lb.|
I don't see any tags here. See, if I pulled up Greatswords though
|Battleaxe||10 gp||1d8 slashing||4 lb.||Versatile (1d10)|
|Flail||10 gp||1d8 bludgeoning||2 lb.||-|
|Glaive||20 gp||1d10 slashing||6 lb.||Heavy, reach, two-handed|
|Greataxe||30 gp||1d12 slashing||7 lb.||Heavy, two-handed|
|Greatsword||50 gp||2d6 slashing||6 lb.||Heavy, two-handed|
|Halberd||20 gp||1d10 slashing||6 lb.||Heavy, reach, two-handed|
|Lance||10 gp||1d12 piercing||6 lb.||Reach, special|
|Longsword||15 gp||1d8 slashing||3 lb.||Versatile (1d10)|
|Maul||10 gp||2d6 bludgeoning||10 lb.||Heavy, two-handed|
I mean... look at those tags. Heavy property, right there. Easily seen and referenced.
So, if I make a greatsword out of volcanic glass and it has all the same stats... it has the two-handed and the heavy propery. And so a halfling wouldn't be able to use it without disadvantage. But, shocking I know, "Metal" isn't a tag in any of these sections.
I mean, look at that Maul. What is it made of? Wood? Metal? Stone? I am showing you every single bit of rules text and there isn't even a description of mauls in the book. If there is supposed to be some tag telling us what everything is made of... then we have a lot of missing rules. How have we gone so long without noticing that?
Unless... there is no tag. There is no requirement that materials be set and immutable. That, in fact, you are wrong and I have provided all of the rule text both for the maul and half-plate, and either could be made of any materials.