Thanks for the feedback! We completely agree that the current way of rearranging slides leaves a lot to be desired. Especially for decks with a lot of slides. We have it on our todo list to switch to a more traditional drag and drop interface which should make this a better experience. Paired with that, we want to change the layout of slides when arranging from the current horizontal strip to a grid of slides that makes better use of the available space.
Presenting all slides in a grid should be a good way to allow quicker navigation outside of the editor too.
Adam: This is still something we want to add but it hasn't been high enough of a priority to be implemented yet. Changed the status from "planned" to "backlog" to better reflect this.