Good angel?

[BG-57]

Let´s SUPPOSE then it has meaning.Let´s see if we can find more secrets with this hypothesis.

Speculate away. It's not like I'm stopping you.

Yes, because two of those Shivas (what you've just stated) are based on GF, they both have the same objective = same entity, you can even control them. The only reason why they look different is because they came from different FF games.
The help from that angel is entirely different.

My point is just because angels look different from game to doesn't mean they're not the same thing. As you said, each game has a different design and look, so they're naturally going to vary in appearance.

Try to compare from the other FF little helpies for the final battles to the angel in the final battle of FF8. So generally, it has to be plot-related.

Of course they may serve a purpose beyond just gameplay, but I don't see why they have to.