Arcell hit what i wanted to say pretty well.
Again, and i can't say this enough, it largely depends on the group you are in. It's up to your leader to decide 1) what strat you're running 2) possible deviations to that strat
if you don't like how it's being run. either leave or start your own group.
Player skill overrides most things. due to latency and skill some players may not be able to hit and run effectively. what works for you doesn't work for everyone. some groups off the wall strats are successful. others they are not.
I'm willing to try any strat with any player. but not everyone likes to do that. some people dont' like running content over and over again trying to figure out exactly how to get off the wall strats to work. they find it a waste of time and would rather just do what is known to work. there's absolutely nothing wrong with that.
there is somethign wrong with someone joining a group. saying they have DRG, WHM, and MNK available. and then complaining they have to go WHM when the group needs a whm and already has 3 DRGs.
the reality of the situations is, if you only want to play one job, only level one job. if you leveled all jobs trying to figure out which job you wanted to play, just say the job you dont' want to play isnt' geared, or dont' mention you have it.
as someone who runs events and has organized PUGs i can't stress how infuriating it is for someone to say 'I have drg, whm, blm, brd, and war' and then ask them to switch to blm and hear 'i don't want to play blm. mnk will work fine' it's not their decision. it's mine because i'm leading the group.
usually I will ask to see their gear. if i think it's up to par i'll allow it. but more likely than not i end up saying. 'sorry, i need you on blm if we're going to win this. we're cutting it close as it is. I know you don't want to play blm but i need you to decide if you'd rather win this fight with us, or try the fight with someone else with a questionable strat. not all of us have 4 hours to waste trying new things'