LibreOffice Calc absolutely chugs when it comes to recalculating. Entire sections of the economy run on large, complicated Excel sheets; porting them over would not only be slow, cumbersome, and time-consuming, but would require hardware that does not yet exist to run them on.

THERE IS NO REPLACEMENT FOR EXCEL in the financial sector. Part of the reason why is because Excel has customers -- big, rich, important customers, and lots of them -- and so it is supported and updated as if by an entity that wants to please its customers.