You are reading right. Actual Yield numbers are designed to shock you

If you don't want to get shocked, look at Gross Yield, that tells you
the interest you received as % of average outstanding principal then annualized based on average age of the loan. Loss Rate tells you
the principal lost to default as % of average outstanding principal then annualized based on average age of the loan. The Actual Yield is just the difference between the two.
This measure works great for portfolio performance (Prosper uses it) as most loans have starting and ending outstanding balance but becomes little wonky for historical loans as the typical ending outstanding principal for majority of loans is zero (except loans that defaulted).
You want to focus on maximizing Gross Yield and minimizing Loss Rate when you read those numbers.
All measurements (ROI, Cash-on-Cash, IRR, Gross and Net Yield, NAR) being used for these loans have their own pros-and-cons. There is no one standard way of measuring performance of these loans. In the end what matters that you should get back more than what you put in adjusted for time value of money.