Iron Age boost on the very large army is 5% if I remember right, you don't need any of the military GB's for it, it'd probably require diamonds, but it's doable. If you have rogues and a 15% boost you should be able to win easily. I think 2 of each wave are rogues so you most likely could go through it with catapults, just using tavern and potion attack boosts.
If you've gotten to a later age/era and haven't developed any military GB's then you dug that hole yourself. If you want to do the daily challenge without missing any then you should adjust your city accordingly. It's just another part of the game that you need to plan for if you want to be successful at it. It's also a clever way for Inno to push a more balanced gameplay. I think strict farmers have trouble realizing that if you also build up your military abilities you can handle the lower goods production with relative ease because your going to be spending so much less of them. So there's an initial hesitation to doing anything military related in their cities which is why threads like this pop up too often.
Rogues and 15% boost is more than most anyone is gonna have in Iron Age. :O
But regardless, the point isn't that it's "impossible", it's that it requires FAR more investment in one area of the game than ANY other daily challenge. It's not even about completely ignoring military, even if you're doing "some military, some trade" you'll still come up short on "Very Large Army" unless you've been camping in that age for a long time.
Every other daily challenge is pretty doable regardless of how you play. Collect tavern silver, gather goods, pay coins, win some battles, visit taverns, spend forge points, and so on. All pretty simple stuff that anyone can do no matter how they build their city. Certainly no GB requirements or diamond purchases.
"Very Large Army" is a significant outlier in this regard, that's all my point is. If you're ok with that, then that's fine. It's people claiming that it's NOT different that seems absurd to me because it absolutely is.