You can't be serious man. Frost Titan freezes a creature on attack, which is basically the same thing as blocking, but better in many circumstances (worse in a few). Wurmcoil Engine, Baneslayer Angel, and Griselbrand gain a ton of life on the attack, which is similar to blocking a large creature. Sheoldred reanimates a blocker every turn, and kills an opposing attacker every turn, all while attacking. Grave Titan makes two blockers on attack, Inferno Titan kills multiple guys on attack or kills them outright, Battlesphere can leave blockers behind on attack or kill the opponent outright, Elesh Norn cripples/kills the opposing team and pumps your own while attacking. I could keep going. Aetherling having vigilance is nice, but it still pales in defensive value to most other finishers in the cube.
This is the part of my post where I reiterate that Aetherling is a strong card and possibly worthy of inclusion, but there are definitely some things he doesn't do as well as other ~7 mana finishers.
Quote from eidolon232Imo this is the best blue creature that costs > 6 mana and I wouldn't mind running a single 7 drop in blue. However blue already has Upheaval, Karn (which technically is a colorless card, but very frequently ends up in the blue decks) and whatever big artifact creature you end up picking in the hope of opening a Tinker later.