What is XLSX?
XLSX is what Excel has written since 2007 - not one file but a zipped folder of XML, with the sheet in one part and the strings in another. Its famous trap is dates: a date is stored as a plain number of days, and only the formatting attached to the cell says it is a date rather than a quantity.
What is TSV?
TSV is CSV with tabs, and the swap removes CSV's worst habit: prose is full of commas and almost never contains a tab, so fields rarely need quoting at all. It is what you want when the data is text-heavy and the quoting keeps going wrong.