Advice for a bad player

So i recently rebooted playing this awesome game, and have been trying to get into multiplayer, learning with each loss. Was wondering if any on this forum could lend their thoughts and advice to the scenario below (which I lost).

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I played a 1v1 Black Forest against a Britons player, and we both boomed up to Castle then Imperial without too much drama. I was playing as the Mongols, a civ I've heard have a very strong late game, and I tunneled towards getting a Elite Mangudai and Siege Onager composition to hold the chokepoint through which he started applying pressure. The issue was this guy was using almost nothing but trash units (halbs, eskirms) with a few E longbows and some trebs to take out my castles. Despite the massive KDA disparity (I had maybe 600 kills and lost 120 military units) he just ground me out of the game. I already realise that not answering with my own trash was a big mistake, as I had so much food and wood lying around, but I guess my main question is what trash units should you opt for when you're sure that your gold-heavy units are more powerful? If i knew how to macro I would've kept my Emangs and SOs alive, but in the moment I just didn't think building six barracks and spamming pikes/halbs was a winning option. Anyone here have any advice on which units I could've used as fodder? Thanks alot