In structural engineering (bridge design etc), we use quite complicated spreadsheets for calculations; a database wouldn't be the right tool for that job. We use excel because everyone knows how to use it and it's easy to print to PDF and see the inputs and outputs and any graphical summaries you have added. Using a spreadsheet makes it easy to check and easy to adapt/change when you want to do a slightly different calculation next time.
I've tried building spreadsheets of similar complexity in libreoffice and it's true they are very slow in comparison and more prone to crashing.
Libreoffice works well for some tasks and I enjoy using it at home but honestly if I tried to use it at work it would cut my productivity significantly. I'm probably using it more intensively than most people though.