I think Takua has been a Toa before the other Toa came. But when Tahu and the others came he became a Matoran because he lost in a battle against Makuta when Takua was actually a Toa of Light. Where else do you think his yellow feet come from ?

Wait, there is more

And actually when Takua lost the battle against the Makuta before Tahu and his fellows. Then Takua´s Mask  of Light was scattered.

I dont see how this solves anything. Have you got any proof of anything like this happening or is it just a guess?

dunno, its in theories... oh by the way, good theory!