The Amazons got their weapons from the InuYasha
There must have been a rummage sale of surplus weapons no one was using that Hippolyta and her army stumbled upon and decided to buy as many magic powered swords, arrows and bees as they could. Since these weapons could easily turn mountains to dust and slay an army of baddies in seconds, this explains why the Amazons had no problem dealing with fighter jets and tanks.
The comic was actually written by Granny Goodness.
She wanted to both insert her own FanFic
into Diana's continuity
and was under orders from Darkseid
to weaken human minds in preparation for Final Crisis. That and she got tired of DC fans calling her a "withered old bag" and decided to screw with them as a lesson in respect. So how do you like that, my little ginger snaps?
- Darkseid : Excellent work, Granny...(his eyes light up)...except to inspect your work, I was forced to read that steaming pile, and this MAY NOT BE FORGIVEN!!!
There is actually an-in universe rationale for that pile of monkey-crap!
Seriously, think about it. Final Crisis reveals that Darkseid's fall, back to around Infinite Crisis, damaged space and time on levels we can scarcely imagine, tipping the balance between good and evil firmly in evil's favor, so it isn't impossible that everything that happened in-between is a direct consequence of that.