So, can we just ban damage meters already.

[Taika]

I find it odd to read that @ 450ilvl it should be impossible, since that is at or even above the minimum item level stated by the duty finder.

It's because the content is balanced for a higher item level than minimum requirement (and also to higher item level than what is available for players when the content is released) and even at that higher item level it's designed to require 90% optimal DPS play from DDs and tanks.

Edit: I managed to find the original quote from 2015 (source):

For development, such as with Bahamut's Coils, the development team assumes what the item level should be for general equipment on players when they clear a raid. They sum up the basic DPS for four DPS and tanks at that assumed item level and cut that by about 10-15% for the minimum clear DPS. Healer DPS is not taken into account when this is set.

Certainly for people who are at world's first level, their goal is to clear it at as low an item level as possible, lower than the one assumed during development. So if you look at the fight and figure out that if it's not numerically possible to clear with four DPS and tanks, you'll need to make up the gap with DPS from healers.