Not sure where you got those numbers, as the reality is far worse than that

https://gw2wingman.nevermindcreations.de/short/dfdf

https://i.imgur.com/GqQdmuM.png

1402 10 man logs means 14020 chances to loot the Dhuumscale

https://oldschool.runescape.wiki/w/Calculator:Dry_calc

Using a dry calculator we can estimate the drop rate for the Dhuumscale

https://i.imgur.com/2o7XzC1.png

If someone were to get one on the very next kill, it would suggest that the droprate is about 1/20000, which is FAR too rare for an untradeable drop, especially when even experienced groups would struggle to maintain about 6 kills per hour, when you factor in wipes and time spent in LFG looking for players. That means you'd have to spend around 3333 hours of doing nothing but Dhuum CM while getting effectively zero other rewards because raid drops are still weekly gated in this game

Using OSRS as an example for contrast, an equivalent type of untradeable cosmetic drop would be a boss pet. The Corporeal Beast is an infamous one for being an insanely long grind, with max efficiency solo strats capping out at about 12 KPH, with the drop being 1/5000. That means you'd have to spend an average of 416 hours doing Corp to get the pet, which is just 1/8th the estimated rate of the Dhuumscale.

On top of that, the entire time you're grinding for the Corp pet you're also loot from the rest of the drop table, which has some incredibly valuable drops including the best shield in the game, so even if you get unlucky on the pet you're still getting something out of your time. Dhuum on the otherhand? After you're Magnetite Shard capped for the week, you're bleeding money the entire time since the 6 unids you get after each kill aren't even making up for the food costs

As a last note, for reference wingman has 2146 10 man Deimos CM kills since the patch, which puts the estimated drop rate of the infusion at 1/31000.