@Jens_Rasmussen @Owl @MeBigbrain
>the world in a non-age of fire state would be cold, dark and practically uninhabitable?
That's what the "Gods" (read: Gwyn and his 45 children) want you to believe. It's called Dark Souls, not Dark Pill (fully aware of the cringe at play here but bear (the curse) with me). The world in the Age of Dark WOULD be cold, dark and uninhabitable ONLY to being aligned with Fire - ie. the "Gods" and their offspring.
The Age of Fire is effectively the Age of the Lords (who were Hollows before they acquired the Lord Souls), but the Lords aren't immortal (just like the Dragons and unlike the Humans), they can be killed and their Souls will eventually find a new host since they're too powerful to just fade away but it's not exactly reincarnation either (unless we're talking about Manus but that's more or less thanks to the Dark Soul being a special kind of Soul).
During the war against the Dragons Gwyn conscripted countless humans into his army and realized just how powerful they were thanks to the Dark Soul's potential being effectively limitless as it's capable of multiplying by splitting into countless fragments, creating life and growing stronger no matter how tiny its fragments are.
This realization led to the creation of the Darksign to contain/limit the Humans' potential by weakening their fragments of the Dark Soul and rendering them mortal - but the Darksign's power gets weaker as the First Flame fades, thus rendering Humans immortal again. H O W E V E R the Darksign is also what causes Humans to go Hollow as it slowly feeds on Humanity. That fucker then psyopped the Humans by creating a religion centered around the Lords (and their children) (the Lords aren't Gods, they're only worshipped as such) and started his anti-Age-of-Dark propaganda to ensure that people would keep trying to link the Flame forever. Oh and he basically erased the Humans' contribution to the war against the Dragons from history.
The First Sin isn't just the unnatural prolonging of the Age of Fire, it's also the creation of the Darksign - what Gwyn had done is worse than genocide.

Dark Souls isn't about resigning yourself to your fate/nature (unless you're a Lord), it's about surmounting overwhelming odds both as an individual and as a collective and how karmic retribution is unavoidable - but you'd better get to it sooner than later, Humanity is immortal but nature isn't.

In other words, the Lords of Fire are Humanity-enslaving kikes. But sooner or later the propaganda machine will break and Humanity will finally say "No." - even if it might be "too late" (DS3, the Age of Dark will still come but the entire world is irreparably corrupted and dying, something something strip mining for EV batteries and chopping forests down/replacing fields with wind turbines)
The entire series is a hopeful warning.