Yes it would be nice to hear from GPG or Stardock on whither they consider this a bug or not.
I've yet to fight against this but, it's not a cheap thing to do....
Please note that the costs listed below are just numbers I've made up off the top of my head, I'm at work and I don't recall what the actual archer idols cost.
Siege Archer Idol's
~550 for level I, 1050 for level II, ~1550 level III, 2050 for level IV
Total costs:
~$5200- 1105 (half price for the ones you sell) = $4095
That's not a small amount to pull off this tactic and on top of that if you kill the lower level archers, they can't resummon them, they only can resummon the highest level, unless they want to pay $4095 again!
So while I'm pretty sure it's a bug, it's not that effective or cost efficient.
-Jara
PS: Every Demigod has AOE attacks/answers. If someone is doing this, it's time to adjust your strategy to improve your AOE attacks and just kill his minions. But frankly if he has 4095 gold to spend, he's going to get some nice war gear or multiple higher level minons that he'll be able to resummon.