You're right. I'm still working on this guide and that is one of the things that I found that made the 40% CDR relatively useless, but it still made a difference when making multiple picks or peeling more often.

In an extended fight I can see the merits of a 40% Thresh Build. However if you have an advantage over the enemy most team fights will be over relatively quickly that by the time you get your abilities back up there will only be at most two extremely weakened enemy champions on the field. If that.