I think relics should be right there to start the moment you finish the MSQ in a fresh expansion. Either that, or it should progress in parallel to the normal difficulty raid. I don't think it should be BiS at any given time, though. Serious raiders should get their best gear from raiding, not from content specifically designed for people who are looking for a grind.

Take this current iteration where non-Savage players had to wait 7 weeks to get a 330 weapon or challenge Shinryu EX for a 335. Since Shinryu EX is the hardest trial before Ultimate, non-Savage casuals probably are positioned at Susano EX, which is 320, conforming to the normal Omega raid armor item level and Lakshmi accessories.

My proposal would be that right at this stage, non-Savage players grinding on the relic should get a 330. If you can beat Shinryu EX and get the 345 weapon, then basically you should be a Savage level raider anyway. So the non-Savage raider either farm O4N for 7 weeks and spend 1k Creation or put in the hours and grind the relic. Most people in this group will probably choose to grind the relic and spend the creation on armor and accessories.