What's the sweet spot for Transcendence?

The rune seems strong on paper, but seems so hilariously outclassed by Celerity in every regard. Surely there must be some use for it; Riot wouldn't make a slot with three options and have only one of them be remotely viable.

Is it best to take it and get a strictly 30% CDR build to maximize item slots? Or does Celerity beat it out even then with the massive damage and speed amp over the value of a freed up item? Going for crazy high excess CDR for its own damage amp seems like a waste too, missing out majorly on the movement speed and compromising the utility of your build. And going just a bit over the CDR cap by rounding out your build with the necessary items like , , or whatever an ADC or fighter needs to be viable doesn't give near the same value of Celerity's combination of stats in the same exact build.

It just feels like a trap rune. It has a slower return value than Gathering Storm and even when it gets to that value it's still outclassed. The only way it can be viable is on pure AD tanks into a retarded-ass pure AD opposing team by stacking s