It depends on how you calculate the percentages. "Percents" are only useful as a tool for small numbers, say less than 10%: 90% is not far from 1/110%, so no matter how you calculate 10% loss or gain, you'll get numbers that don't stray too far apart.

Probably the author means that 79% of the money they paid (8.8/11.1) was thrown away, thus it was only worth 21% of what they paid.

Stating they paid almost five times too much is much clearer.