Plenty of veterans can tell you stories about Nekusar, the Mindrazer being enchanted by Corrupted Conscience, or how a sneaky Tainted Strike ended a game unexpectedly
This deck died down over time, especially when Mox Opal was originally banned (Mox Opal is back, but there are plenty of stronger combo options in Modern than Cheerios)
Perhaps not good enough as a scry commander, but Arwen is a solid role player, even if you never activate that 6-mana ability
For example, it is possible at any excavation point in the combo to not reveal any eligible monsters that can be summoned, something that can cripple the Deck from as early as step 2
They cannot
If you dont see this as the centerpiece, then the fact that its cost is very flexible should still make Oona a very desirable card for some control and mill decks