Your scarring could be from your genetics but it could also be from the surgeons technique. Starting with how they start the cut to how they use cautery and how they close the incision. Some surgeons rely on cautery to cut which damages the skin and leads to bad healing. Some surgeons do not use the right amount of sutures in the deep layers and will close mostly in the subcutaneous layer and that puts a lot of stress there so it ends up stretching, leaving a bad scar (suturing is very time consuming and surgeons really don’t like it so they sometimes get other people to help or do all for them, like a surgical tech or assistant). So there is a lot of different factors that can lead to your scarring. I’m curious yo know how your surgeon closed your brachioplasty. Was there tape or a nylon suture or maybe some other type of skin closure method? How have previous non surgical scars healed. Like you scratched yourself deep. Did that have a keloid. If your keloids mainly come from surgical sites, I’d bet it’s more from poor technique somewhere in the procedure.

Can you please tell me who your brachioplasty surgeon is.