Long time FCP (since v1.25) and FCPX user here.
Last year I did a project in DaVinci Resolve – a music performance, and the
client requested a separate clip for each song. It was VERY easy to output all those clips
using Resolve. And yes, it did take a long time to find the beginning and ending of each clip.
I am surprised that FCPX is taking so long after the first couple of clips. I would take a different file and attempt to do the same thing on 5 clips and see if the experience is any different.