Yes, I know full well how to war with a backwards lead troop, but that's why I advocated cavalry...they're way more versatile against more advanced troops

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You could probably avoid getting economics all the way to flight if you want, and that's a worthy beeline.
But economics has very little outlay as a tech/civic compared to building castles everywhere, and it's usually easy to trade for it no matter your path if trades are on.
Also, if you delay it when you could have gotten it first you add a merchant to the opportunity cost of delaying it to use castles. Castles aren't holding a lot of economic water here.