If this were true they would not allow premade parties to deviate from 2/2/4 structure. If this were true it would not be permitted to use a solo-tank strat on Twintania (yes, it exists, I've been in a party or two that's employed it, though it didn't quite work out for various reasons). What happened here is a simple case of "Ramuh has no actual direct damage attacks, so Titan-egi can ignore 90% of all damage dealt by Ramuh". That's not the devs "making you play it a specific way", that's players bypassing several fight mechanics because the developers made an oversight. This is players discovering a way to entirely excise not one, but TWO entire classes from the Ramuh fight, and in doing so make it EASIER to clear. And this has happened less than a week after the implementation of the fight. You and I both know how this game is. If Square didn't patch this and FAST, it'd become just as hard to find a Ramuh EX party allowing tanks to join as it would be to find a party willing to try and deal with Allagan Rot hot potato.
I think the strat itself is cool and clever, but this should not and will not last, and you don't have a leg to stand on if you're going to claim that it's being shuttered and restrictive to not allow a strategy where the hardest non-Coil boss currently in the game can be tanked by an AI that takes 10% normal damage from EVERYTHING said boss does.
