I give it a pass because it's doing complicated things, it's free software and I also temper my expectations slightly because it's a Java GUI application (and I expect those to be slow).
I would certainly not expect it to be more performant than Office '97.
It would be great if LibreOffice had a spurt of speed-ups. Kind what the browser wars also competed fiercely about.
Word 97 was basically feature complete though (if buggy - the same bugs persist today of course), including track changes and compare/merge documents. The killer feature now is being able to work on the same document with multiple people and seeing their changes in realtime. You used to be able to do this on-prem but that product (Office Online Server) got killed. I wonder why.
Unless you use a lot of VBA (and you can't translate it to Python), or you've got some proprietary COM addin that you can't live without, LibreOffice's Calc is a pretty damn good replacement for Excel for the majority of users.