Honestly, even if the trip is longer than 40 minutes, which sounds very likely (Cleveland to Dunwich takes 30 minutes), it's still worthwhile having a tourist service from the CBD to allow tourists to access the bay islands practically from their hotel rooms, rather than having to hike out to Cleveland for it. Think of it less as a commuter service and more like something similar to the Kuranda Scenic Railway - yes, you can get to Kuranda in 35 minutes by bus and for much less money than the 2 hours by train, but for most tourists KSR + Skyrail is still the way they want to get up there.