I agree. Having a higher base AC doesn't necessarily make the armour "better". Also - lighter armour implies advancements in armour 'technologies' - there's a reason all modern armour are lighter than traditional ones - advancement in materials and designs.Well, I’d argue 12+Dex AC is actually better than 14+Dex (max +2) AC with disadvantage on Stealth.
If Brigandine is like Scale but yet more advanced, it could be modeled in D&D mechanics (mechanics that are often far less than ideal when it comes to realism or historical accuracy) by being lighter.
Obviously reworking the armour list to an entirely different set of names would probably be "better" (from a historical perspective, at least. Some people care more about D&D 'tradition' than historical accuracy.)