This does seem a bit pants to me - especially if you're playing a game at a higher difficulty level.
There are plenty of games I've been in where I've had no iron, and had to build up an army of pikemen and bowmen to hold off the AI swordsmen. This adhoc army always proved somewhat fragile but workable when defending. If I could hold out till rennaissance and bulb rifling, I'd upgrade and make the fragile army more robust. I haven't got the game yet, as I'm in Europe, but this swap to lancers seems like a serious shot to the foot. Screwed for iron, fine, you're pretty much screwed for long term army build.
I can understand the "historical" logic of it - but there's plenty of stuff in game that doesn't follow exact historical patterns. Maybe when I play, and see the new balancing, I'll find it's possible to fight with lancers. Alternatively, the diplomacy system might now work and I might be able to trade for iron.......which would be a whole different game. I'll wait and see.
What I liked about vanilla though was that in one era you might be screwed for a particular resource militarily, but if you survived that era you'd be able to make up for it in the next era.