Well, here you're making an assertion that
Tulkas "would" have done something, which, I'd
say, does not mean alternate scenarios (including
the one I raised), are unreasonable in themselves.
In other words, they might be unreasonable to you, yes, because you think (your opinion) Tulkas "would have" killed
Morgoth. I, however, do not think Tulkas
need have killed him, and the honor was given to Turambar.
Well,
Tolkien himself characterized it as a
mannish myth. Do you disagree with Christopher Tolkien's commentary concerning this?