Could the gems buy a set amount of factory time instead of %completion? The way they are, they actually get less valuable in terms of time saved the higher your factory level! Also, using %completion, it's always the same price to buy any color block with gems.
The "+10% Progress" feature of the factory is just temporary to convert gems into resource blocks during the early game and will not stay this way in the final game. You are 100% right, it is completly useless in the late game.
For those of you having trouble needing lots of shots and overheating with high level weapons, try focusing on speed first! Slowing down the enemy ships makes it so much easier to hit. Getting high level engines before weapons helped me a lot.
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The "+10% Progress" feature of the factory is just temporary to convert gems into resource blocks during the early game and will not stay this way in the final game. You are 100% right, it is completly useless in the late game.