I am the Hammer. I am the right hand of my Emperor. I am the tip of His spear, I am the gauntlet about His fist. I am the woes of daemonkind. I am the Hammer.
I agree, that the proof is in the pudding. Where do you live? I have a solid 1500 point allc omers BA army list, I would gladly put up against the green hoarde. Rather than mathammer it out, why don't we just put both armies on the table and see if the army holds it's weight?
I will gladly record the Battle Report, and post it here to vindicate you should you be successful in defeating my army. I mean, people can flame you all day, but maybe you have something here. I suppose I can lead my BA like lambs to the slaughter againt the might that is the green assault horde.
So back onto the whole: how to beat mobs of orks things:
Its really just about focusing fire. Obviously the IG are on off the best at it. Deployment can also be your friend against masses of orks: Almost every deployment results in the Orks being staggered in their assult, that means one must simply prioritize targeting.
I'm not saying its the easiest thing is the, and obviosly some armies are better at it then others, but I don't think my IG have ever lost to mobbed orks.
My standard all comers 1750 list has 4 large blast S8+ Templates, I take a squad of mortar teams, every transport has a heavy flamer, and every squad has a flamer.
DWs: Prussains. KoW: Elves WM: Khador WHFB: Dwarves WH40: IG, SM
Games-workshop: changing the rules one new codex/army book at a time.
It's also about blocking their movement and delaying them. Fast moving Hellhounds are a great way of delaying an Ork Hoard. The tank is too dangerous to let live, yet it will take at least 2 turns of close combat to kill it. Which ties up the Ork Hoard's front rank and forces the squads behind it to go around the melee. Allowing focused fire to be more effective.
Sentinels also work wonders here. As do sacrificial infantry squads. You can kill my guys all you want in close combat. But you're going to do it one squad at a time and waste a turn on each, with me firing on you the whole way.
Bolter spam and flamers always worked for me to kill massed Boyz.
For Guard, I always wanted to try manticore spam. 3-9 S10 AP4 large blasts per turn? Nasty, even with cover saves.
The mouth of the Emperor shall meditate wisdom; from His tongue shall speak judgment