Its because their formats are really fast. We had a somewhat similar conversation about
greater gargadon a year ago.
In a slower format where you can build the counters up to 4-6, and still be in the game, it would be terrifying.
I don't think it's comparable to Gargadon at all. Gargadon even in my environment rarely becomes a creature. It gets played as a sac outlet mostly (one that cannot be removed making it valuable), but it's durdly and I can see it being not so great in a fast aggro based format.
Aether vial is none of that in a midrange/control deck. It's the opposite.
Sure, it's a worthless top deck, but so are most 1 mana cards. Toss it to draw spell or something and move on. In your opening hand though, I don't care how fast your environment is, putting stuff into play for free with no timing restriction is extremely powerful (actually, it's broken). That card breaks the resource mechanic of the game wide open. It functions as a mana rock that can be upgraded to continually cast bigger and bigger creatures at instant speed for no cost whatsoever.
This card in my opening hand is doom for my opponent. T4 utility dude, t5 dude, T7 finisher - all free - while I am using my mana to cast other business spells, other creatures, etc. That is going to win most games. Ever have a control deck that just can't find that 6 land or double swamp or whatever ? Cast Cataclysm and still drop 5+ drops. This card is retarded.
My 2 cents is you guys should build a deck with a bunch of creatures that is control oriented and put that card in your opening hand and see how many decks can beat you. It's going to be a short list no matter what your cube looks like.