Beginner/noob aoe2 battle question: how to turn the tide

Hi dear AoE2 reddit,

I want to preface my post with:
- The last time I had played AoE I had no man-hair at all. Now I'm in my thirties. I've downloaded the game for my gf initially, but I started hogging her pc to play it. So I have it on my pc now.
- I cannot manage to beat the new AI on moderate.
- Thanks to the internet, youtube, and being an adult, I have found and read:
https://www.reddit.com/r/aoe2/comments/1c7zwe/how_to_not_suck_at_aoe2/ & http://deathray.media/aoe2
- I have watched:
The importance of patrolling & Beginners guide to countering every Unique Unit [AoE2] & Beginner guide to counters in AoE2

I have (for now) worked around the issue of early death against the moderate AI by having three teams, lock teams. The AIs usually fight each other first, then finally I have a 1vs1 against AI when I have resources and a good position/protection of the city.

Problem:
The scenario is always the same: eventually the AI starts attacking me with an endless chain of: special civ units, knights/paladins, onagers-rams-trebuchets, mostly. Depending on the civs there can be other infantry, skirmishers, spearmen, etc.
It does not matter how many towers, castles, walls, troops, I build/create.
We always come at an impasse where I end up just spamming new troops and throwing them on the battlefield. Sometimes I manage to hold my ground, sometimes the AI manages to break in and do some damage, I push them out, I repair things. Rarely I manage to gain some ground and do a small attack on their front, but it's in no way as severe as what the AI does to me.

During my very last game I had to give up because I had finished all the available gold. I was then producing only trash units, and eventually I finished all my available wood. I had no wood available to chop anywhere on my side of the map!
I thought: well, you didn't secure enough resources before the enemy, and he beat you. But I checked the statistics after the game and it wasn't true. I had collected twice as much wood and food and stone as the enemy. He collected three times my gold - the fact he had all the relics played a role.

Question:
How do I break this situation? Is there some strategy that I am missing, or is it about the micro management of the troops on the battlefield?
I understand that i need to collect more gold and relics, but this battle situation cannot be explained by a lack of gold.

Thank you.