There is also Blick which launched recently which claims to be very very fast https://blickeditor.com/?lang=en and part of recent wave of fast software (Task Slinger, File Pilot)

Neither open source nor free however.

The fact that they reimplemented everything from scratch doesn't give much confidence. The last thing I want to deal with in a video editor are bugs from code that's seen less real-world use, originating from who knows where.