The Relic and Eureka are just fundamentally incompatible.
Eureka is hardcore grinder content. It requires a lot of time spent on it and it alone to gain any progress, while unable to do anything else during downtime because you have to remain in the instance at all times.
The Relic, on the other hand, has always been a Casual content. A way for non-hardcore players to work towards getting a decent weapon, by doing content they already know, and know they can do. At their own pace. A dungeon here, a roulette there, and whatever else you want to do while you wait for the queue to pop.
By locking the Relic behind Eureka, who is it for now? Hardcore grinders. The primal weapons are for Extreme trial runners, and raid weapons for Savage raiders, where does that leave the Casual now? Tomestones alone, I guess?
