See, you're implying that as soon as they make their difficulty adjustments that all of the players everywhere are just going to log in and find all the Second Coil gear mysteriously in their inventory and have access to the Final Coil already open to them. This is simply not the case. Also yes, they play catch up. We're in Final Coil, they're messing around in Second Coil catching up to the rest of us. See how that works?
I'm trying to help some friends of mine that never cleared Twintania to take it down so they can move on because they want to get to Second Coil. They don't go into the fight and Twintania just drops dead for no reason. They still have to handle the initial pull with the Scourges. They have to get through Conflag/Fireball phase. They still have to dodge Divebombs or risk being thrown into a wall that will instantly kill them. They still have to deal with the snakes and try to take them down before Aetherial Profusion. Still gotta dodge Twisters or die. Still gotta burn down the Dreadknights. Still gotta handle Hatch and Liquid Hell (although that phase was pretty darn easy even before any adjustments).
The fight is easier because the damage dealt to the tank between Death Sentence hits is largely inconsequential, as the tank's increased HP and the healers' increased cure potency trivialize most of it. DS/Plummet/Attack in quick succession can still be tricky, but for the most part there is less stress there. The DPS checks are much easier. When I cleared T5, we had to 4 stack Conflags. Any less and Fireball could kill people. Any more and the Conflag would blow up too quickly. Now, a 3 stack conflag is normal. Easy to take the hit and survive, easy to burn down the conflag before time runs out. In fact, sometimes the conflag dies too fast. We had a fireball target run in to the conflag like they were supposed to, but the conflag died before Twin used Fireball and wound up getting the two people who got broke out killed by it. After those first two phases, though... they still have to get around all the instant kill mechanics. It is still a learning process, just not quite as unforgiving of one. Plus, they can just "turn off" the Echo and wear nothing but i90 gear to get the true "T5 Experience" if they so desire.
At any rate, there is no "instant win button". If you're new to something like T5 and think you're just gonna waltz in and beat it without a fight because you have an Echo buff, Twintania will still destroy you without so much as a second thought. Similarly, I can't imagine that Second Coil is going to be instantly trivialized the moment they make their proposed adjustments.