I'm not particularly keen on the idea that the OP has proposed, though I understand where they're coming from. I don't even have Second Coil unlocked and I can see their concern that Echo will make some of the boss fights more difficult rather than easier.

I invest a lot of time into FFXIV each time I log on.However, I have not been able to do T5 because nobody wants to do it. Why? Because as the stories go, Echo actually makes Twintania more challenging (I think it has to do with raid wiping for pushing phases, as has been experienced with other bosses in this game).

I came close, though, for my character on Behemoth. Members of my FC were going to join with some members from our "sister FC" to get myself and another player past T5. And then the two of us would most likely be sitting in the Sister FC's second static group. Sadly, I was the only one that showed up on the appointed day and time. The other person didn't log on at all. I keep hoping for another chance, though. Maybe I'll get it when 2.4 drops.