Eureka! summons a copy of the minion, so it keeps card advantage. You play three cards from hand with this. Also, this is a one-of, whereas you can have two Eureka!s in your deck. Eureka! is also a lot cheaper, enabling combos. This is purely for board.
Not that this is bad, it's just different. I wouldn't throw comparisons around like that.
I would expect this as a Epic rather than a Legendary Spell. It is a good card nevertheless but the warrior will need some big minions to make this work. Damn, I was so expecting "Summon 7 Boombots with Rush" as his Legendary Spell.
Different applications. Eureka copies a card, which means the original is still in your hand, which is great for specific cards you want to play several times. You can cheat out a minion already on turn 6.
I don't think this card is good, I don't see the application of this card except those random dream scnearios where you load your deck with high costed cards.. you need to play something in the early game to get there you cna't afford to run so many minions that cost enough to justify this card.
9 mana is an awkward mana cost, it does have synergy with the new card omega assembly, but I think it's quite mediocre otherwise, costs too much, plays into AOE, missing battlecries.
Wow, I can't believe I didn't even think of that. This would work great if you ended up discovering 3 mechs that total more than 9 mana. That would be one hell of a board swing. The obvious downside would be if any of those mechs had a battlecry.