Encounters need to be designed to let people play the class they want to.

[Rydin]

This is ALWAYS going to be an issue in games that don't want to make every character made homogenized. There will always be some form of efficient setup as a result. Short of a debuff to power for overusing one specific class in a party, or requiring use of specific classes to do something, it's almost impossible to guarantee balance for any one thing.

Doing any of these things to prevent the "preferred" setup just makes the game overall less fun for everyone. Sure it'll get you into that event/fight/whatever easier, but it'll exclude others at the same time, almost to a degree of necessity. "Sorry, we can't invite you because we already have a <insert your class>" or "LFM need <least used class> so we can start the fight".

From the developers standpoint, you ask for the impossible when you ask too much. You don't want homogenization, you want there to be prevention of preferred setups that excludes your preferred playstyle (even though outside of the preferred, you still do fine), yet you still want them to treat things as though it were.

I would not be surprised if folks actually think it can be done in one days work to balance the game out. Thinking that it takes no thought at all for developers to, for example, make any fight in the game automatically adjust the difficulty according to party member classes, levels, gear, etc. That it's just a simple matter of typing "balance" in a single line of code. That'd be awesome, and probably would put a large number of people on an unemployed list, but that's not how it works.

What about something like this:
Taken from this thread

Imagine a boss who had a shield... and with that shield, he took very little damage. So you have a Lancer use the Vorpal thrust>Impulse Drive>Chaos Thrust Combo. If the chaos thrust is executed on the shield arm side, you get the message "Shield arm appears weak and shaky"
When that happens... a marauder uses Maim>Godsbane on the shield arm and the arm falls, Defense is reduced 40% but attack speed increases 10%
those are arbitrary numbers... The point is you make the fight doable but very difficult without completing the special objective... and easier but still tough when you do complete the optional objective
He still wouldn't be an easy fight with the incap but he'd go from being stupid hard to just Ifrit hard.

Then when his HP fell below 20% he'd put up a magic Ice paling. The only way to repel the magic paling is with a Battle regimen that had (in this order) fire, wind and then concussive blow
Fire to weaken the ice, wind to intensify the flames and concussive blow to shatter the paling
With the paling down... his defense and magic defense go down 25%
(again arbitrary number enfeeble, but you get what I'm saying)
You could make the debuff 50% decrease in defense... whatever....

At 10% HP, his regen increases. The only way to mitigate that is with Piercing arrow>gloom Arrow>Bloodletter combo
Once again... you can beat him without that. It is just noticeably tougher

The point is you could go into the fight with 5 of whatever class deals damage the best at the time, but without being able to complete the optional objectives, you're in for one hell of a fight.

Also by making multiple objectives in 1 fight... you allow for different parties to fight it their way.

You can say "We don't have a marauder for the shield incap... but thats ok, we've got the other 2 incaps covered.
Or "We don't have an Archer for the 'Final Blow' incap, but we've got a strong DPS team and we can do the Shield and magic paling incaps so we should be good.

This way, you could take a very mixed party and have fun on NMs
Instead of
/shout Ifrit party, 3/8, need thaums only