Given a fast enough computer with a fast and big enough SSD, you can ISO record all the sources. It is very easy to use that to create a synchronized multi-track file in FCP if you also add a “clapper” sound at the beginning to help line them all up.
As for editing, it is not very easy to tell FCP (or Resolve) what to do with the various layers that give you graphics, PiP, Splitscreens and so on.
I think that the ATEM Mini Extreme is a relic of a past era. It’s trying to recreate traditional TV production in a low price setting. Modern live streaming is all about engaging the audience. Once the live stream is over, postproduction adds very little value to the viewers.
Every tool has its sweet spot. mimoLive is best when used live. Not sure what the ATEM Mini Extreme is best for. If you have 8 Kameras, you probably do not want it to be HDMI.