I'd just like to slide in the 2-cents that any skirt wearing lady I've asked about how cold or warm they feel in the winter, are usually warmer than me, wearing jeans. So if you include the climate as part of your building in terms of character's choice of dress, you can reasonably include skirts and dresses. They can reduce heat, like in the desert and hot climates where the sun hitting you does most of the cooking-alive to the person, and they can maximize heat, like on the rugged mountains where the air is thin.
Materials matter too, such as anything that's breathable. Yes the modern stretchy stuff is great for athletes, but they're doing very specific things. Athletes that don't have access to modern neoprene and the like are usually running in loose fitting cotton or wool, depending on if they need to cool or heat their body.
An example of why the Greek gods are always pictured half naked in white robes is 1) material choice and 2) have you been the Greek isles in the summer? It's bright, and hot, and ALL THAT WATER. That's also why the silk trade was so important to them because suddenly getting a material that was woven could withstand swords, arrow points and spear points to a degree were fantastic. Sharp weapons were deterred by silk and blunt weapons were practically impossible to break through that outer layer of silk.
Also for fighters for designing you need to consider what kind of combat are you subjecting them to? Most of my fighters are in either the magic realm or sword/spear realm, which allows for a good 2ft of space between you and your weapon. Ease of movement can be adjusted to become more tanky vs limiting.
Mage's, if their clothes were realistic over video game stats, clothes should give them tank stats and magic stats (M-ATK+, M-DEF+, and DEF+) but for some reason even though they're wearing piles of robes and such, video games say "those count for nothing for regular defense and you have to rely on magic enchants to boost magic defense only. ARE YOU KIDDING ME? LOOK AT MY MAGE. HE'S A WALKING CLOSET AND A BED. HE'S TANKIER THAN THAT GUY IN THE TIN CAN (who is not withstanding a horse charging him at full force like a jousting tournament, good god, developers).