Except for the fact that a main portion of the complaints around previous Relics was "I want Relic but don't want to farm old content"
So, it's exactly comparable.
Farming old content, extending its lifespan by breathing new rewards into it (Effectively like "Adding" new content by increasing the pool of relevant Dungeons/Trials) was something that enhanced gameplay. Something that was removed at the behest of people who complained about having to do that for the Relic.
One could use the exact same arguments as are being made for Eureka exclusivity on Relics for keeping Relics behind old content.
"You don't NEED the Relic"
"Don't like the content? Don't play it"
"Relic is supposed to be a grind that isn't for everyone"
Eureka is not designed with the Relic in mind. In the same sense that old content farms were not designed with the Relic in mind. Just having the Relic being exclusively earned from Eureka doesn't make it designed around it any more than Tam-Tara is designed for Zodiac weapons because you can farm up light there.
Nothing about Eureka explicitly is designed around the Relic. The story is mostly focused not on the Relic, but on the zone itself. The Relic isn't necessary at all to progress through the content. The Relic barely interacts with the content (Just the Elemental Bonus eventually). The Relic grind itself doesn't use anything that is unique to the content (FATEs/Light farms are not new. Neither is farming for items such as Logos Actions).
Just because the devs say "We designed the content for the Relic" doesn't actually make it so. If they had actually utilized unique Eureka only systems for the Relic grind (Such as needing to beat X, Y and Z enemies with your Elemental Wheel set to elements A, B and C, or with Magicite set in specific ways as opposed to stacking 5 in a single element to swap around for max damage with additional Magicite (That is attained through RNG currently...) being set to whatever the corresponding defence up will be) then this argument might have more merit.
However, as it stands, there is little difference between Eureka and previous Relics. Only that, inexplicably, instead of getting its own rewards (Which I advocate for) the Dev's got lazy and slapped in the Relic and removed the multi-faceted way of progressing such items that existed prior.
If, Eureka had been given its own, unique reward instead, this entire topic wouldn't exist. There wouldn't be an argument about Relics. There wouldn't be all these people complaining about Eureka (Aside from the "We lost content because of it!" thing, exacerbated by old content not being stretched out by Relic progression being tied to it). No-one would care that Eureka had exclusive rewards that could only be attained via grinding Eureka.
That is the crux of the issue. Instead of bothering to create new rewards for the new content, the Dev's decided to take an existing reward and stick it behind the new content. Not because they want to do something new, not because they feel the unique content is an interesting system for Relic progression (Since the Relic progression is largely unchanged from previous, in the sense that it's merely just FATE/Light farm stages ad infinitum) - Given the way that the Relic currently sits within the content. But because they're seemingly trying to entice people into a type of niche content that has failed previously as well as reduce the work needed to think of rewards by just taking another existing reward from somewhere else.
It's more akin to if in ShB they made PvP top 100 rewards come from farming in a open world PvP zone. Where PvP enthusiasts then start complaining about having top 100 rewards no longer being tied to top 100 status and being told "Why do you need those rewards?" or "You still have wolf seal rewards!"