FF14 WoL leitmotif context - spoilers

Torn From the Heavens:
This is the "generic" boss music of the base game. It's hard to call anything in this game generic music given how many unique themes there are for everything, but that's the best I can do for this. Notably, it plays when you come across the more elusive world bosses (FATEs) that often give you an achievement for killing them. What better way to introduce the leitmotif than when you come across a real gameplay challenge!

Penitus:
This is the theme for the big finale dungeon of the base game before any patches and future expansions continued the story. By this point, you've gone from adventurer to hero, so it's fitting that this theme takes your "warrior of lightmotif" (couldn't resist) and evolves it. The music flows nicely on its own, but it syncs up very well with the dungeon too. Parts of the song loop until you reach checkpoints and then the next part plays. It really makes you associate parts of the song with parts of the dungeon.

The Maker's Ruin:
From a gameplay perspective, this is the first phase of the final boss of said dungeon. It's a really fitting story battle and is quite the showpiece when doing the content at a similar power level to when it was released. For all intents and purposes, this is the final boss, which makes your theme very fitting here. This also comes after the dungeon has been teasing you with it up to this point.

A Land Long Dead:
This is the theme for a dungeon that appears two expansions down the road. It has a glaring callback to Penitus in it. This is because the dungeon leads you into the reappearance of one of the characters from that big story dungeon two expansions ago. It's quite a nice touch by Soken. There's also a linked thread in that the weapon you're trying to stop in the Penitus dungeon is old technology, the same kind that you see around you partway into this new dungeon.

Heartless:
The final boss of the optional raid series in the same expansion as A Land Long Dead (Stormblood). The gist of the story here is that the boss is an AI whose core programming is to become stronger. It spends the entire raid trying to understand where your strength comes from and adjust. When you finally hit the finale, the AI decides to mimic humanity to try to find the answer it's been looking for. Another great touch by Soken is that in mimicking you, it also mimics your theme song.

From the Heavens:
This is noticeably similar to Heartless because it's found in phase 2 of the harder difficulty of the same raid boss. For those who complete the first phase, they get an extra little cutscene and a new boss to fight with its own music.

More Than Truth:
Featured many times in the story of the latest expansion (Shadowbringers), this theme normally plays when interacting with your "doppleganger". Without giving too much away, he's almost like a reflection of your possible future. Naturally, Soken graciously thought to bring back our leitmotif for him. His presence is rather melancholy, which explains the tone of the song.