Charcharo said:
OK new tactic! Their tech is good enough to create Tesla Coil weapons, right? Lightning guns mounted on Baneblades with tactical giant laser assaults should cripple the first 2-3 ork waves. Then we flame the ENTIRE battlefield (except our side) and retreat to a fortress. Then we start sending small 100 megaton nuclear bombs across the battlefield.
See, Orks aren't that stupid. They know the idea of tactical retreat, even if it's just their instincts and subconsciousness. After all old Ork saying goes:
"Orkses never lost a battle. If we win we win, if we die we die fighting so it don't count. If we runs for it we don't die neither, cos we can come back for annuver go, see!"
Plus you just get rid of single WAAAGH force, few years later a new one will pop out from all the spores. They were created to fight long before other races of WH40K universe, rumors say even to fight the first Necrons and C'tans. Pretty much once a planet gets infested with Orks, it stays so until destruction of that planet. Even if the current WAAAGH moves elsewhere there will be enough of marauders and remaining spores to create another WAAAGH years later.