Well, I'm not sure how your group works, but I wouldn't bring a melee just for turn 5: I would have had them in the group prior to that. If they have a really geared alt, then sure I'd bring it but most people do not. Sounds like a similar discussion we had a few days ago...
Can be done, yes. Should be done? I don't think so. I'd rather have two magic DPS and two physical DPS (one with melee LB) for turn 4. Many groups have cleared it with 4 melee without issue. Same with T1. There are many different strategies but one that seems to work out every time is a melee to balance the DPS on both snakes so that they die at the same time.
I also don't want to have more than two people fighting for gear. You can load your group up with 3 BRDs and a caster DPS, sure, but I'm not so sure they would appreciate it when 2 others are lotting on the same gear they are.
So not only are there practical reasons for not wanting to stack classes but there are also logical ones as well.
Only case you have is turn 2. In which case, I'd still prefer a melee on the left side to push ADS out of a certain phase with the LB. Our monk happens to blow both bards and me away on left side ADS as well. Yes, the BRDs have to focus on silence and I have reduced damage due to left side's nature but ignoring his DPS is annoying as well.
Your statement "Level 3/levelwhatever melee LB is not needed" is just flat out wrong as many groups build strategies centered around it including turn 2. You don't really need black mages or summoners either as you've indicated on turn 4 yet it isn't necessarily a wise idea to neglect a certain job because you will need one of them eventually. People said the exact same thing about DRG before they knew much about how effective their synergy is with BRD on turn 5. "You don't really need one." but it happened to be quite useful later on.
In fact, I believe he even said: http://forum.square-enix.com/ffxiv/threads/113554-Letter-from-the-Producer-LIVE-Part-IX-Q-A-Summary-%2810-30-2013%29
Regarding stacked party compositions, it's actually more beneficial to have different jobs in the party to help fill your limit break gauge faster. There are a lot of situations where you can use level 3 limit breaks, so if you have a strategy that calls for limit breaks at certain times, it's be more advantageous to make parties with different jobs.
All they've said about BRD is the incredible burst they're able to do in a short amount of time was too strong. This perhaps says to me, "Prempetive PVP balance" more than PVE balance because short bursts in PVE are only talked about when it comes to things like conflag or maybe Titan's gaol/heart. However, they've also acknowledged that ranged have an easier time avoiding attacks and mainly use Titan as an example. But, he has also said, "Stop sucking." in many instances too...
We often hear opinions that Titan is too hard, but looking a people who were participating in the Titan Challenge we held at multiple events, not only dragoons, but everyone in general had their cameras zoomed in quite a bit. I believe this is because in FFXI and FFXIV 1.0 you couldn't zoom out very far, but in order to dodge different attacks in high level encounters in FFXIV: ARR, it’d be best if you zoom your camera out to the maximum distance.
Also, as a melee DPS, I think it's difficult to avoid bomb boulders while focusing on your attacks, but ranged DPS and healers can maintain a fair bit of distance and there may be other players in your party who are good at dodging, so if you don't know where to go you can follow these players to stay safe. Of course it's important to memorize the patterns, but quick decisions are also critical.
As for this little piece:
With a little luck BRD can go a long way over BLM or MNK DPS.
Our BRDs parse below me and the monk on several turns every time with the same gear (or better). They generally do very well on turn 2 if we use PLD silences instead. Yoshi also stated: http://ffxiv.zam.com/forum.html?forum=152&mid=1386216713100624973
What about black mage?
Yoshida: For black mage, there's a bug related to casting speed which has put its DPS ahead of other jobs. In patch 2.1, we'll be fixing this, which should put the overall DPS of a black mage on par with that of other DPS jobs.
I feel like your theoretical situations substantially deviate from what has already been observed to be effective. Edited, Dec 13th 2013 4:51am by HitomeOfBismarck