The main difference between armor is mostly revolving around it’s purpose.
However, the difference in defensive values, commonly accepted by historian (i am one) differs wildly from era, location and timeframe. the French where known to make some of the best armours, the italian were pretty close as well and had some very interesting designs. the gothic and german armour it too had some merits, but each ‘style’ differed in it’s factors defined by whom they expected to fight against, what types of weapons, the fighting style, horseback on not, etc… For instant, the french knight where much more willing to fight on foot - something that reflects in the design in comparison to the gothic style.
However, simply saying X is better than Y is wildly wrong. it would be like saying “Bullpup rifles are better than then revolvlers.” different ideology, with different design and reasons.
Insofar as brigandine is concerned, that mostly evovled out of poorer people, who could not afford armour, just riveted, sowed or otherwise attached plates (not always uniform is thickness or size - or even matierial) to a leather sheet, or other material. Over the years, and by the time this game happens, the brigandine fill in the roll of a cheaper version of plate, with advantages in flexibility (but a good plate specificly made for a person would have almost no problem in flexibility) and a few other areas. The technology for making brigandine evovled to the point where was not considered a ‘poor man’s amor’.
What i am saying here, is that there is no better. Like the sword vs katana thing that dacrimal referred to above - they are different with different ideologies and reasons for making them the way there are. Simply put, you cannot compare katanas and longswords, bastard swords or otherwise and claim one is better. They are different and are not filling the same specific role. The same aplies to armor, they are both different and apply and use vastly different concepts that give rise to a piece of armour with different attribute and strengths.
edit: also I would like to add that mail was very goot for defense against slashing, but almost useless against any sharp points such as arrows, bolts, etc… However, gambersons (or alternatively spelled gambeson) were very good at stopping arrows. These were usually home made by the solider himself or his wife/mother and thus varied significantly in construction and quality. Some used different formulas - tight sheets of linen sown together, others added a couple layers of leather, others added padding and fillers. So the combination of gamberson + mail (maille) gave the soldier a very good, all-round protection. However, and especially with crossbows, it did not always suffice. That is why we see a drastic increase in armor following the increasing spread use of the crossbow and other more powerful bows and missiles around the 12th century.
edit continued: in regards to the OP’s question above. my answer is no. They are different and not necessarily better. In-game this is not reflected as it is a vastly simplified version of real life attributes, concepts and otherwise. Though I think it is faithful in it’s representation of the basic role they fullfilled.
Plate is also much thinner then most realise and can be easily dented. The main advantage usually arise from what we would now call a “deflection angle”. The bows and striges slide or bounce of rather then their force be complete absorbed. This allows for much lighter armour without compromising defence value to much. However, if struck at just the wrong blow, one can easily and severly dent plate armour. This is not true across all models and styles though but more of a ‘rule of thumb’.
