Psynaptik we've implemented a few things recently which should improve your experience a fair amount.
r61 introduced caching to cloud saves, so now it doesn't need to request a file list every time you open the dialog. The cache lasts for the duration of the session, and can be manually updated by pressing the refresh button in the dialog. This can also be turned off in the settings if required.
r64 introduced folders (finally). It's been a fair while coming, but hopefully this should make your folder saves a little less "haphazard"!
This still doesn't really solve the "slow file list" issue, I marked the github issue as closed as the original reporter never got back to me on trying to improve the performance. It would be greatly appreciated if you could help with that, as it seems to be related to certain accounts so we can't replicate it.
As for the "default" option issue, there isn't a default. It just shows whatever the last service you viewed, or the source of the current project.