Jesus Christ, when did Bay12 get full of Tumblrina Social Justice Warriors? Seriously, taking inspiration from Medieval Europe is making them sexist & racist?
Anyway, on point. With regards to character traits, I can see upsides and downsides to making them either static/moveable, and potential ways of addressing both. Personally, I like the idea of character traits remaining static. It adds more strategic depth, in my opinion, forcing you to very carefully choose and adjust your party composition in order to succeed. Prevents you from 'putting too many eggs in one basket'.
Also, as Rap said, for better or for worse, character traits define people. If you present a method which can lead your zeroes to heroes, you'll find yourself with a very copy/paste army of superstrong, eagle-eyed, heroic roidheads, and for a roleplaying game that's generally considered a bad move. In KotOR, FF, NN, FO, your party, your companions, are all different. Not all of them are heroic, many have weaknesses, but it doesn't stop them from being badass. Not one bit. It makes for a far more gripping story, even if it's one that we the players project onto the game ourselves.
Archer A has the one-eyed trait, takes a shot at the enemy Lichking, has a 3% chance of hitting, succeeds kills him. On its own that's not exciting, but the player can spin that into the tale of how William the One-Eyed slew the Lich King from two hundred paces, turning the tide of the battle. With games like this, part of the enjoyment comes from making our own tales of heroism, and overcoming unbeatable odds, being the underdog. It's cinematic. Yes, in the real world, people change, and a fat man would turn fit through constant battle (unless he also raided the supply wagons after battle, but I digress), but in the cinematic world it's one thing that doesn't really get taken into consideration.
Besides, who said that being fat, and a coward, means you can't be a badass?