Midgardsomr and the Sundering (Spoilers)

[Seraphor]

Why would they have developed differently? The split created identical copies...

No it didn't. Each shard had a different elemental alignment, or rather, each had a different element with a majority influence.
Elemental aether has an effect on the world around it. A little extra water aether and a certain creature might get a drink somewhere it wouldn't. A little extra fire aether and a fire spreads a little further than it would have done. So on and so on, butterfly effect.

[YianKutku]

No it didn't. Each shard had a different elemental alignment, or rather, each had a different element with a majority influence.
Elemental aether has an effect on the world around it. A little extra water aether and a certain creature might get a drink somewhere it wouldn't. A little extra fire aether and a fire spreads a little further than it would have done. So on and so on, butterfly effect.

Pedantically, when the split happened, the shards were identical.

The differences in aether happened after the Ascians tried and failed to Rejoin the Thirteenth, which caused the Flood of Darkness, and also threw the aetherial balance of every other shard off. (Through some as yet unexplained mechanism where the aether of one shard affects others, which is also how Rejoinings and Calamities work.) We don't currently know if Midgardsormr came to the Source before or after the Thirteenth fell to Darkness.

[Cilia]

I can't comment on the "power level" of dragons as compared to the races of man (particularly since aetheric soul density doesn't seem to translate to higher power), but...

Considering that Hydaelyn sundered Zodiark, the "will of the [planet]," the sundering phenomenon is more likely to be localized than not. Further, Midgardsormr's pact is explicitly with Hydaelyn, so he'd have had to appeared on the scene at some point after the Sundering.

Make of those what you will.

[Eloah]

In the context of the game, when someone refers to 'this star', it actually means planet or world, not a sun/ball of gaseous plasma undergoing nuclear fusion reactions (this pops up quite commonly in manga and anime, which I understand is due to the Japanese language not having a specific word for 'planet', instead using a word commonly translated as 'star', but I dropped out of my Japanese language class so someone far more knowledgable on the subject would be better able to clarify or deny that).

Either way, the Sundering only resulted in Hydaelyn the world being split into the Source and 13 shards. The dragons were not sundered because they are not native to Hydaelyn and arrived on the Source long after the Sundering occurred.

I can confirm that, yes, the Kanji used for star (星) also means planet, or more specifically a light emitting/reflecting heavenly body. The main distinction would be that the word for star is the Kanji by itself, and is pronounced as ho-shi (ほし). But when the Kanji is combined with others to create a myriad of celestial objects it is often pronounced as se-i (せい) as in the actual word for planet (惑星) wa-ku-se-i (わくせい).

The English word Star is actually very similar but is actually a homonym. It comes from the Ancient Greeks who first discovered the concept of planets, noticing that they moved across the night sky. The term used to describe them was, planētes asteres, which means wandering stars, or simply planētai, wanderers, for short. It isn't used as often today, but it still sounds "old timey" so that's probably why it's being used in FFXIV.

[TinyRedLeaf]

One of the wonderful and thought-provoking observations from studying real-world history, is the links we can often see between ancient civilisations and cultures.

Most ancient civilisations discovered or adopted technologies like iron weapons, the wheel, road and bridge construction, and so on, at roughly the same time in history. The same can be observed for ideas like religion, although those tend to evolve more quickly to better reflect local socio-geographic conditions.

Similarly, the kanji for ( 星 ) as most of us would know, comes from Chinese. The same word was used — and is still used today — in China to name the planets. Mars, for example, is 火星 or the "fiery star" in both Chinese and Japanese. That shouldn't be surprising — Japan adopted the Chinese writing system during the time of the Tang Dynasty (618AD to 907AD), and it was also around this time that Buddhism came to Japan via China.

My hypothesis is that both the Greeks and the Chinese likely influenced each other, in their observations about the "wandering stars", and came to similar conclusions that they are planets, or special stars.

The term is anachronistic today, given what we now know about planets. But the use of "star" to refer to planets really isn't limited to just the way the Chinese and Japanese name the planets — it very often appears in English literature as well. So it really bemuses me why some people are so confused about the term. They are effectively synonymous, from a literary point of view, even till this day. It's not just "old-fashion speech".

[Kesey]

I can see why we're splitting hairs here regarding full extent of the sundering, but I think the game has been pretty clear that Hydaelyn split "the star" which I interpreted to be the planet into 13 more dimensions and the dragons have said numerous times they showed up after the sundering and made a pact with Hydaelyn to protect the star.

Where I read into this discussion, is the amount of power the dragons have are extraordinarily great, so without an actual lore official source saying otherwise, I'd assume the dragons are not sundered because they were on another planet that wasn't sundered. This would fall in line with their power level and the Ascian machinations around their eyes in Stormblood as a key resource to accelerate the war in Ala Mhigo as well as motivating the church in Ishgard to also accelerate the Dragonsong War.