You can’t capture with AE, and the way you are working is how most people do it. You are right to be concerned about the quality loss of exporting to AE, then rendering from AE and bringing that file BACK into FCP. That’s a lot of pixel-trashing, and while using a 10-bit codec (like Blackmagic 10-bit) for these transfers/renders will help to minimize quality loss, you pay for it in hard drive space, heavy files taking longer to work with etc. etc.
There is an After Effects plugin from Automatic Duck called Pro Import AE that allows you to import your entire FCP project file into After Effects. It uses the original source footage like FCP does, and basically recreates your FCP edit on the After Effects timeline, including fades, dissolves and most effects. This way you eliminate that render from FCP, and can finish projects in After Effects.
https://www.automaticduck.com/products/piae/index.php
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