Those crispy banana chips you buy are deep fried, not dried. Dried bananas are chewy like yours. I like to add some lemon wash before drying, so they don't o as brown, but it's purely cosmetic.
Time to dry also relies on humidity, and if you're sitting under the same weather pattern as Melbourne at the moment, that sounds about right. Try it during one of those hot weeks in Adelaide, with the wind from the north. You won't even need to turn the dehydrator on!