if you read them you'll see that they do blend well

it sounds like you won't, but I have read everything published and the numerous magic systems all feel very unique, but are based on a very sound central logic

one of his foundational tenets in writing magic systems is something like exploring the limits of a magic system before you expand it, and he absolutely does that

mistborn's second trilogy is a perfect example of that, there's not new magic, or at least not much of it, but a remixing of what was in the first trilogy and all of the implications of that remixing was more than enough for the second trilogy