I have gotten an Ice Devil with a Wraith Sword and Boots of Flight by turn 16. Then turn 17 Alteration 2.

It is more than possible with some nations; and it isn't that disruptive to your economy as you need your economy to build the slaves and research needed.

The primary issue is you need a nation that is naturally strong and has significant surviviability in their normal units.

They key is not to overexpand. Though personally I don't like putting all my eggs into one type of basket Which is what you are doing, however that Ice Devil crippled 1 opponent and allowed me to be much larger and stronger than any of the other players by turn 25.