When I linked izanagi and the jubi, I meant the following:
1. The jubi's body is far from earth.
2. the rinnegan has no relation to the jubi (they're completely independent)
3. nagato's power is tiny compared to that of the so6p
4. from 2 & 3, nagato cannot summon the jubi from that far
5. madara may need jubi's body to recreate the ten-tailed beast
6. from 1, 4, 5, madara has to remake the jubi's body from scratch.
7. madara should probably use izanagi to do 6, as there's no other similar technique
I didn't mean that the jubi was initially created by izanagi. Actually, I'm sure it wasn't.
Now for the whole gedo mazo vs jubi discussion, I can't agree with most of the arguments.
I'm a bit reluctant to pursue it because I believe that the jubi is not gedo mazo just as much as I believe that tobi is madara.
Gedo mazo:
1. an independent summon. Has to be, since the rinnegan is independent from all previous things. The rinnegan was not born as a response to the jubi.
2. nagato should probably be aware of what he summons, especially big things. Therefore, he should know what the BIG gedo mazo was. If it were the jubi, he'd probably call it that way. A beast does not name itself, so the jubi probably doesn't have more than the name we all know.
It's like trying summon a toad and you get the dead demon instead.

3. Tails don't just fall off. It's the great JUBI! I'm sure it's more resilient than that. And gedo mazo does not have tails.
4. Gedo Mazo is summoned by the outer path, not the animal path. So it's not like transporting it from a place (moon) to another. And we have to admit that it was inside the moon in the first place. again: nagato's powers are nothing of that scale, we all saw that when he tried to contain the kyubi.
5. I don't believe that nagato put 9 eyes on top of a bandage that covers the jubi's big eye.
6. The stubs that appear on gedo mazo and those that may be present on the jubi's body may be simple coincidences... just like so many other things in the manga. They're not even outlined. How could we tell what those are?
... but I'll admit they look
a bit similar. Still, they have their differences. And quite major ones.