Therein lies the problem.
Said bad players have several options;
Youtube
Reading their spells + Common sense.
If after all that, they can't seem to be performing well...
Then you can't fix stupid and move on.
I agree with you on helping teach others as far as the basics of a proper rotation goes. The strange attack patterns and "rotations" I've seen from other party members have astoundingly went up since Stormblood's release.
The problem is people don't take initiatives to read up guides or desire to improve like you do.
You can refer players to reputable guide providers like MTQCapture, MrHappy, Xenosys Vex, Graehl, or some detailed written/video guide that literally spills the secrets on how fights work move by move, phase by phase. The issue is that the people who could use the battle hints still don't want to spoil or improve their knowledge of the higher-end battles.
You can provide links to the best linkshells, free companies, discords, or other forms of voice chat to communicate, teach, socialize, and/or share new stuff that could help improve gameplay. The problem is that some of people who probably could use those mediums to improve simply do not care at the end of the day.
My Happy may not have the most ideal guides ever, but he does explain the gist of how the boss battles work, albeit nowhere near as detailed as MTQCapture or Xenosys Vex.
I do remember the Garuda Extreme guide Mr Happy has been criticized for. Mr Happy's guide had the MT tank both Garuda and Suparna. That would mean a Double Wicked Wheel having a high chance of killing non-tanks (heck Garuda's Wicked Wheel alone would knock out a non-tank at the relevant item level 65-90.) However, no other video guide showed that the "intended" triangle stat that JP players tend to use to minimize stress on the main tanks and melee players.
I will say that Mr Happy's best written guide IMO is his Sophia Extreme guide. That guide showed the square tiles being used as the place to stand while there will be a small tilt happening, among other things. (and those areas are where the waymarks were placed at the time the battle was relevant in 3.4 and 3.5 patches.)
MrHappy isn't something I'd call reliable as far as guides go.
Not interested in teaching someone who doesn't want to learn.
All I can say about this Matter is, dont stop to help even if you meet people that are rude, if so thats their loss, not everyone is Like that. If you dont help people because you think most of them dont want help its the same as if you were that Player that dont want to make an effort to learn. Because you dont want to make an effort yourself.