Yup, definitely easiest. (That's how I first got it too.) Dunno if it's ethymologically correct, though; that depends on what the roots of "pain" are.
Since it's explained further down the page that it comes from an earlier loan from Latin "peona", "punishment", I suppose there is kind of a cognate in English itself from the later loan of the same word that has lead to "penalizing".
Since it's explained further down the page that it comes from an earlier loan from Latin "peona", "punishment", I suppose there is kind of a cognate in English itself from the later loan of the same word that has lead to "penalizing".