Please read my post again, because it seems like you failed to understand most of it.

Coil is not the current Raid tier. It was designed for ARR when the level cap was 50 and your gear item level was much lower, not for Heavensward or Stormblood. So of course it will be easier to do today unsync'd with higher gear, and of course it "isn't the top grade Raid anymore," but there are still some fights and mechanics that aren't trivial no matter what your level is. Just a few weeks ago there was a thread asking devs to either nerf T9 or remove it from WT. Because people seem to think you can faceroll it when you cannot, and I like that it is still challenging even at level 60.

If you want to run this content sync'd down to level 50/minimum ilvl, use Party Finder to find people that, like you, would like to run Coil sync'd. Just know that it will still have the echo buff, and may still be missing core mechanics back from when it was the current tier. If you want a real "uber" challenge, then why don't you try Second Coil of Bahamut Savage as well, sync'd down with a group. And I'm sure the reason Coil was nerfed so much is probably because people complained about it being "too hard." Just like they complain about everything else being "too hard."

I don't know any other way to say that Alexander and Dun Scaith are used for current, end-game progression, where as Coil is not. Coil is now used as a way to get Wonderous Tails stickers, or a quick unsync'd clear run-through with newbies for bonus poetics. It is also used for glamour, tank mount farms, and for aetherstones/orchestrion rolls. And of course, the story. But even still, it isn't that surprising that a Duty Finder queue may never pop. And comparing it to content that is 1.) used for current progression, and 2.) not even that dated (Dun Scaith is only a couple months old) is not a fair comparison.

The devs don't need to do anything to Coil. As much as I would like for it to be restored to its original difficulty, or at the very least give an option to run it without the massive Echo buff, it's unlikely to happen. Because the developers are more focused on developing content for 4.0, not upgrading/downgrading older content. I guarantee you once Stormblood is out and people start getting to level 70 and geared, the same thing will happen to Alexander. And the Void Ark 24-mans.

Which brings me back to the Party Finder. Want to run Coil as sync'd down as you can? Then make a PF. I promise you it's not that hard. And it's even easier now than it would have been before cross-world PF was a thing. So take some initiative, and make a PF. Trust me, if you tried pugging sync'd T5, T9, or T13, I highly doubt the majority of the runs would end in a clear. Because people just want to Zerg everything, rather than actually do more than press 1-2-3.

And I still stand by what I said earlier: if you want to challenge yourself at your current gear/item level, try two-manning T5 or T13, and then come back and tell us how easy it was.