Eureka is meant for casual players.

[Joe777]

But the difficulty of said content is still subjective. What one person finds easy another may find hard. Generally, the "casual/hardcore" labels come from what the majority considers the difficulty to be. To which I would say that Eureka is neither. If I had to pick I would call it "Midcore" content. It's like PotD floor 150-200. Many consider PotD in it's entirety to be casual content but the difficulty for those that do not know jumps in the later floors. It takes skill to beat it. And if you're rocking PotD solo, I would deem the challenge to be more hardcore than any Savage content.

Right now while it people are farming it in masses, it might look casual to some. But in a month or two when the content dies and someone wants to go inside, it'll feel like Savage to them taking on NM with only 2-3 parties in their instance.

Eureka is hardly midcore. Overall the mobs are weakerish than trash mobs in dungeons, but tougher than overworld mobs. Using the magia board properly makes enemies even easier. Some jobs such as RDM or any healer can keep themselves alive easily long enough to kill mobs 1 on 1. You don't need to be pro to solo Eureka, but you do need to be above amateur level.