Oh, definitely endgame and beyond material, for sure.
Arguably the three most powerful Relics in the game will definitely be really hard to get, and not possible to obtain until endgame areas open up.
Those would be the Celestriad, Master's Scroll and Iron Duke. I'd also personally put the Soul of Thamasa, Wring, Bloodlust, and Minerva's Plate into that top tier of Relics as well. I'd list their effects, but it's more fun to let the players learn what they do on their own.