Min-maxing is always going to happen, but that doesn’t meant that it’s a good idea to make it easier to do. The degree to which this is possible and what form it takes is very important to how a player learns to play the game. Right now, looking for the best possible synergy in traits and backgrounds isn’t really a thing, because it would take a long time to get it right and then your starters might die anyway. Making it easier would suddenly make it much more of a factor in how the game plays and how it should be balanced.
The point of mentioning Dark Souls is that it is a great game that doesn’t allow everyone to play as they like. Take for example how it has no save at will and no multiple save slots for the same playthrough. You could argue that putting it there for people who want to use it couldn’t hurt, because they just want to try to play in a different way and everyone else can choose not to use it. However, this would result in a fundamentally different game with a different atmosphere to it, even if you don’t use it, because choices that cannot be taken back are different from choices that you could take back if you wanted to. You cannot skip out of restarting at a bonefire if you die. You cannot take back attacking Gwynevere. You cannot see both endings without playing the game again. This adds a weight to the actions that you take that is only possible because of how the game does not offer you a reset button, which would result in the game undermining the sense of inevitability build up with the games overall design.
Jagged Alliance 2 is a very different game in terms of setting and how it handles recruitment within that setting. Custom characters there are essentially the player using their network to call in mercenaries that fit their needs, because you as a person are larger than the conflict that you are now a part of. It’s the difference between a player that acts more globally and a player who acts more locally. It fits the setting and kind of conflict that is central to the game (hiring foreign mercenaries), so it doesn’t clash with the design. A rough equivalent of this would be to have the player in Battle Brothers be a noble who’s sending out a mercenary company to handle the situation of the area where the game takes place, which would be a different kind of game.
Mods are fine because they aren’t part of the core game. In fact, I’d say it would make for precisely the kind of thing that modders should make. Modders don’t need to think about whether or not what they’re making fits the design, because what they’re making is not part of the core experience, so they can make things that the developer can’t. The developers, however, are the ones actually responsible for this core experience as conveyed through the design of the game. They make what everyone will play and what mods can build on, so they have to be consistent in what tone they set. They are also just a small team and need to carefully decide what features are worth the effort of implementing, because that means not spending time on something else. Custom character creation is simple nowhere near as worthwhile as some of the other things that I’ve seen them mention of considering and would undermine the tone of what they have so far.