The Leveling Problem explained.

[DPZ2]

Because the game never once through the entire playthrough of the MSQ requires you to properly play your job, There never is a dps check or anything where you actually need to think for a bit or practice(excluding certain sequences where you are forced to play different character, so you don't really know what you are doing, and even then you can lower the difficulty in case you fail.)
You can beat all teh trials even if you instantly die because the other teammates just kill it for you.

To some extent, after the changes made to gameplay over the years, this is quite true. Both power levels of attacks and the experience of players make a lot of the instances much easier.

However, with 20+ classes and jobs, creating high-end in-game tutorials for each would require a nightmare in resources, and one that would have to change extensively for each expansion.

I can guarantee that making such a tutorial mandatory for end-game gameplay after each expansion releases would tick off quite a number of high-end players. It would, however, remove the need for the so-called Mentoring System, so that might be a plus.

I'm not exactly sure why the Japanese servers do so well at end-game gameplay, with consistently higher percentages engaging in and completing the content. Are they just that much better at the game, despite the fact that the MSQ does not require you to properly play your job?

Or, perhaps, are they more dedicated to finding and learning from resources outside of the game?

For all of the complaining Rinon does in the two videos mentioned by the OP, I haven't found a single "learn to do better during the MSQ" video. Lots of end-game commentary on healing, yes, but nothing that walks a new player through the best habits to develop for healers while leveling. It's a common fault throughout the youtube ecosystem. Lots of "How to Raid" without any consideration of "how to prepare to raid while leveling". At least most of the jobs mentioned on the icy-veins website (example: https://www.icy-veins.com/ffxiv/white-mage-leveling) provide level-appropriate rotations for the job that will make sense as end-game approaches. Alas, Youtube creators do not yet feel the need to help develop the necessary skills while leveling.

[Eastwall]

To some extent, after the changes made to gameplay over the years, this is quite true. Both power levels of attacks and the experience of players make a lot of the instances much easier.

However, with 20+ classes and jobs, creating high-end in-game tutorials for each would require a nightmare in resources, and one that would have to change extensively for each expansion.

I can guarantee that making such a tutorial mandatory for end-game gameplay after each expansion releases would tick off quite a number of high-end players. It would, however, remove the need for the so-called Mentoring System, so that might be a plus.

I'm not exactly sure why the Japanese servers do so well at end-game gameplay, with consistently higher percentages engaging in and completing the content. Are they just that much better at the game, despite the fact that the MSQ does not require you to properly play your job?

Or, perhaps, are they more dedicated to finding and learning from resources outside of the game?

For all of the complaining Rinon does in the two videos mentioned by the OP, I haven't found a single "learn to do better during the MSQ" video. Lots of end-game commentary on healing, yes, but nothing that walks a new player through the best habits to develop for healers while leveling. It's a common fault throughout the youtube ecosystem. Lots of "How to Raid" without any consideration of "how to prepare to raid while leveling". At least most of the jobs mentioned on the icy-veins website (example: https://www.icy-veins.com/ffxiv/white-mage-leveling) provide level-appropriate rotations for the job that will make sense as end-game approaches. Alas, Youtube creators do not yet feel the need to help develop the necessary skills while leveling.

Because l know people that are even afraid to do story mode content... I have a pvp friend that can't do her relic because she has not done any pve for a long time and is afraid for that story mode trial.... I will help her later tonight.

[Mayhemmer]

It's a common fault throughout the youtube ecosystem. Lots of "How to Raid" without any consideration of "how to prepare to raid while leveling".

That's a thing I noticed when I was trying to pick BLM back up a few months ago. Most "How to [Insert Job]" videos I came across came in one of two flavors: meme videos, which generally aren't very helpful and are mostly unimportant fluff; and "guides" that just recite the tooltip of every job before launching into end-game rotations, just assuming the viewer is already aware of all the nuances of the job's mechanics and how they effect each other, but never explaining them.

Maybe there's stuff out there that goes into that and I just didn't come across it, but it really feels like there's a general lack of tutorial content floating around that actually explains the workings of a job from the ground up. It's very strange considering how popular the game is.

[Arohk]

It's very strange considering how popular the game is.

No , you are correct, the Black Mage job is very unintuitive and badly explained in the game. Also the gameplay style changes completly while leveling.

first you must switch from fire to ice via Transpose, then you get Fire 3 but cant actually use it unless you get a freecast, but the freecast proccs at the very end of a fire cast so you have 0.5 seconds to react and use it, then you get Ice 3 to switch from fire to ice and don't use transpose anymore at all. Also you dont use Fire3 freecasts anymore, you only use it to refrech henochian at the end of the fire rotation.
And very much later you get Umbral Soul which seems useless at first glance but before you get Umbral Soul BLM feels extremly clunky in any fight with downtimes.
The job is fine on high levels but feels totaly trash on low levels.

[DPZ2]

No , you are correct, the Black Mage job is very unintuitive and badly explained in the game. Also the gameplay style changes completly while leveling.

first you must switch from fire to ice via Transpose, then you get Fire 3 but cant actually use it unless you get a freecast, but the freecast proccs at the very end of a fire cast so you have 0.5 seconds to react and use it

To be clear here, the freecast for Fire 3 because of the Firestarter trait gained at level 42 has a 30 second countdown, not 0.5 seconds. One can also anticipate it a bit, since the tiny icon appears before the action icon lights up.

I totally agree that Black Mage feels pretty decent at higher levels, and it does require readjustment once you hit level 50, and again when you hit level 60. Moving from ARR into HW was definitely a relearning experience.

I'd have been quite happy if icy-veins had started FFXIV leveling information back in 2015, but ... at least it's much better now. No thanks to youtube videos, unfortunately.

[Arohk]

To be clear here, the freecast for Fire 3 because of the Firestarter trait gained at level 42 has a 30 second countdown, not 0.5 seconds.

No, you misunderstood, you can get the freecast when Fire is >0.5seconds from finishing the cast, and you now WANT to use Fire 3 and not cast another fire to not waste any proccs because the freecast does not stack like fleeting Raiju from ninja which you can stack 3 charges.

so when youa re lucky with proccs you do Fire > Fire 3 > Fire > Fire 3 > Fire....