I know it is just an ARAM game, but is this impressive for a ratio?

I feel bad. You guys easily won that if your Jhin was there. Though he'd have likely eaten into your kill count quite a bit.

Depends on your MMR and personal skill, plus the champ you were playing (The link isn't working for me ATM)

Although in any case that is an impressive score, even for ARAM.

Le edit: Yes, in the given situation that IS an impressive score.