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.
LibreOffice is good for the home user, hobbyist, and student, but lacks the advanced accounting functions of Excel.
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.