I have tried using Google Sheets for large calculations, with even a few thousand rows it is much slower than say LibreOffice (instant vs. progress bar) Although maybe the WASM thing was not working.
Sometimes Google Sheets isn't just slow, it completely chokes and hangs on large spreadsheets with thousands of rows containing complex formulas. Excel handles the same spreadsheets fast and reliably.
Not surprising, google apps regularly seem to be slow to respond when I just type stuff.