Use the job stones. You lose more than you gain and it doesn't hurt to get used to the job because especially when you reach lvl50++, you basically unlock a lot of skills for you to use. It's also beneficial for you to get a job to lvl60 first for exp bonus, it will help with leveling your other classes/jobs.

Don't get confused by "PLD is easy and boring", Reddit has a lot of veterans so it's very skewed. Most PLDs in game don't even know their simple rotation which is nuts. While Flash sucks, it still does its job just okay. The learning process will take some time for new players. My advice is to keep doing dungeons as a tank because you are taught more about how to be a proper tank than running around for quests.

The general idea as a tank is to take hits and mitigate them effectively. That's your first part to see where to use your defensive CDs, the next few parts will involve intricacies of the tanking role itself because once you are at the top of the chain, the game "allows" you to also dish out huge DPS and help other roles to go off. This DPS issue as tanks has been a controversy time to time due to disagreements and different opinions.