Not every professional user requires the "advanced accounting functions" of Excel. In fact, I'd wager that such features are used only by a small minority of professional users, so LibreOffice should be suitable for most professionals as well.

Regardless, LibreOffice also has full Python support, so really, technically there's nothing that it can't do that Excel can, if you can make use of Python.

Excel is not as good at accounting as accounting software, but it is sometimes good enough.

Likewise LibreOffice is sometimes good enough.