What do you mean they created BG3 from the mechanics of DOS2? Skills aren't on cooldowns, instead of action points there are separate things of movement, actions, bonus actions, reactions, readying am action, help. Instead of classless characters it's now a rather strict class system. Levels unlock skills and features rather than buying skillbooks. Only the wizard has an interest in "skillbooks," and a rather specific group of warlocks. Shadows now play an important part of stealth. Instead of things being pretty strict and predictable, especially persuasion, almost everything is based off of chance now. BG3 also had verticality now. The only similar mechanics are it's turn based, which isn't a new idea by Larian, weapons have a skill that comes with them, and a cone of sight is important to stealth. Mechanics-wise, I think they are very different games.
