That the explanation is that Lanfear burned out when she fell through the doorway, died a bit later, was transmigrated as Cyndane and finally Healed by someone in a way which weakened her somewhat, it doesn't really fit with BS's apparent uncertainty on this topic (even if he is pretty sure).

BS just discussed Cyndane's OP strength with Maria and she apparently clarified its origin. I don't see then why BS should tell you: "If you were burned out and transmigrated you would still be burned out, is my guess ."

As said, another explanation might be that Lanfear was stilled (but by whom?). Or maybe that Lanfear actually wasn't transmigrated (but why the new body then? Apparently the Finn don't have the powers to change bodies). Or Cyndane was stilled and Healed again after he transmigration (but that also doesn't make much sense).

Of course, there might also be another explanation for Cyndane's weakened strength, e.g. as pointed out above her much smaller body.