The problem isn't exactly the drop rate so much as it is the fact that progress is completely at the mercy of RNG; which is going to run the gamut between "I got mine in a day or two" all the way through "cosmic plaything" ie: nothing drops for you, specifically. This does nothing but make it incredibly frustrating for the people stuck on the low-luck end and can even cause animosity.
Relic should have no business being obtained via what is essentially a glorified gacha; not because "low drop rates are bad," but that a "drop rate" shouldn't even be a factor at all for something tied to player progression. It's disgusting that two people can put in the same time and effort, and one can end up with even less than a third of the other's progress in the same time frame, purely because of luck. Leave that s*** to mounts, minions, lvl 1 glamour and furniture.
Saying "you have months to complete it, stop being impatient" is such a strawman argument when some fortunate people can get all of their demiatma in a couple days while it can take over a week for others with comparable playtimes. RNG grinds are the laziest grinds to implement, and doesn't even turn out to be a "grind" for luckier people. Same people also don't have to sit on their tomestones because they've already unlocked the ability to buy the Arcanite to save-up for their next relics by running their roulettes or even participating in South Horn's CEs, being allowed to kill several birds with one stone. Meanwhile, those with no such luck will likely sit @ their tomestone cap, waiting for RNG to decide when they can start utilizing them in the same way.
If everyone had to spend the same amount of time with the same effort for this progression weapon, I don't think the backlash would have been nearly this large. The RNG atma system should have died with ARR and HW; the fact that the devs made a joke about it in the cutscene showing our characters' exasperated reaction shows that they know the players did not like the system but are just too creatively bankrupt to come up with anything else and had to resort to this for retention. Let alone innovate on it even a little by giving a pity trade-in system to alleviate particularly bad RNG.
Naturally, they couldn't address that fact in the Live Letter, and had to hide behind a question asking to raise the drop-rate instead.