No need to prune. This is really a cosmetic issue more than anything....the spotting doesn't really affect how the plant grows......just how it looks :-))

Just clean up and destroy all the foliage when the hydrangea finally drops its leaves. And a fresh layer of mulch surrounding it can prevent splashing of any spores that remain on the soil.

I have noticed that, this wet year, leaf spot is worse than in previous years. I do prune the worst offender leaves but I am talking 2-4 leaves per shrub (minor stuff).

Try to limit overhead watering and instead water the soil and never the leaves. That should help minimize the problem too.

When the overhead watering comes from rain....and this year, maybe excessive rain in some areas......it's pretty hard to avoid :-)