You are making them play as they don't wish to play. That's the downside. The same could be said for the reverse of course but all parties have the same option to just drop or to kick. Both of which should be taken as simply a difference of playstyles IMO. No hard feelings, not personal just "I do not wish to play with you for whatever reason".
Also.. why are you coming off so sarcastically? "what joy!" indeed.
I would say that micromanaging a random dragoon for a normal fight is getting far too involved in what other people are doing. Did you pass? Cool. None of the rest should be your concern. Did you fail? If you did THEN it's time to address where the failure is coming from and if super obvious , E.G. the dragoon is visibly not using skills or standing in things, that person can be voted out. You should not get overly involved with how someone else is playing if the content is being cleared in DF. If it is not being cleared to your liking you can remove yourself from the situation and/or give a non-accusatory suggestion. If you NEED things done a certain way make your own parties and don't rely on the game to bring you "good" players.
I have leveled every single job and 2 alts and I can say the amount of noticeably bad players I've had to endure has been 2-3 a week (capping all tomes, doing all weekly lockouts) at most. So personal experiences may vary ( I am on sarg which I hear is notoriously "git gud") . I don't care if healers don't DPS, I don't care if tanks single pull, I don't care if other DPS single target. All of these things will still pass any DF content. If I want things done efficiently I'll make sure that happens myself. If I run a roulette I'm agreeing to deal with whatever I get. Someone is that bad? Kick em or leave. How would you take someone telling you that you were playing your character wrong? Probably not half as well as you say you would.