Actually, I don't believe it... If you're playing on deity level, you need to conquer a civ pretty quick (to get great leaders and more land)... playing with the maximum number of opponents the map is usually filled very fast. The opponents exchange techs very rapidly, so very soon they'll get pikemen and stuff. Even with a perfect start, you still don't have time to build more than 10-15 swordmen before the attack if you want to stand a chance (so you can force him to give away his techs).
My question is now, even if you've got cattles everywhere, how do you have time to build those 40 catapults, 10 swordmen and 10 spearman or whatever you think is a good army? I'm not stupid, I understand 40 catapults are powerful, but when do you have time to build them?
The thing is, many people who say they're playing on deity level play against 4 or 5 opponents on a standard, and I'll tell you, that's nothing... I read the stragedy guide on this page (babylonians) and the guy who wrote it used a simular tactic to mine.
But, I still want you guys to convince me. I would do anything... well not anything but anyway... to see someone conquer the world with 16 opponents on a huge world map using stacks of catapults and cannons... I'm sure someone knows how to do it, would be really cool if someone recorded a game and posted here!