How to defeat this comp

I'm a noob trying to learn this game.. I'm decent early games (1800 elo HD, only 1v1 arabia) but when I try to FFA or something similar, I ALWAYS end up losing in the end, even if I'm in a great position due to my early game. I really SUCK when people start massing units. It seems like my units get demolished no matter what I do.

I took a bad printscreen of the guy that totally wrecked me: 📷https://gyazo.com/8a4e9c2d81cf63e51618fb42acfaad98

So I'm Persians with a lot of gold (I had 30k in the end after investing in spies). and I still lost in less than 10 minutes. The scorpions were protected by the Imperial Camels. I tried to spam halbs, but they died before they even spawned. I tried to push back with Camels, but his Camels are stronger. Paladins/Elephants are obviously a bad choice. He pushed me quite fast with the trebs.

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I realised I had to take out his scorpions but I couldn't do it. And I couldn't push back his Camels without Halbs, which I couldn't produce since he had scorpion. It seems like a catch-22 moment... Not sure how to break this?

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I'm thinking I engage with I'm outnumbered and that is why I always lose end game fights. Maybe I'm too avaricious and should just spam more production buildings and units...

What would you have done? Is it game over at this point and my mistake was letting him produce this army?