These are two different things (and this applies to both 2.8 and 2.10).
All settings that you applied are automatically saved as "Presets" as a single file (tool-options/gimp-levels-tool.settings in this case) in your Gimp profile. Their purpose is to let to quickly store your own settings for future use. While by default these settings are only identified by a time stamp, they can also be given a name for easy retrieval(*). Gimp will let you manage them (instead of editing a file) with the "Manage Saved Presets" dialog.
The Import Current Settings From File/Export Current Settings to File things are (as name implies) mostly used to exchange settings with other Gimp installations, and not really meant to save/restore your own settings, which is better done with the other method. As such the files can be anywhere on your disk (where you saved them from your browser or your mail, or on a network share) and their management if out of Gimp's scope (but I agree that the default directory in the Gimp profile is a bad idea).
(*) and if you use my settings-cleaner thing, those with a name are never cleaned.
All settings that you applied are automatically saved as "Presets" as a single file (tool-options/gimp-levels-tool.settings in this case) in your Gimp profile. Their purpose is to let to quickly store your own settings for future use. While by default these settings are only identified by a time stamp, they can also be given a name for easy retrieval(*). Gimp will let you manage them (instead of editing a file) with the "Manage Saved Presets" dialog.
The Import Current Settings From File/Export Current Settings to File things are (as name implies) mostly used to exchange settings with other Gimp installations, and not really meant to save/restore your own settings, which is better done with the other method. As such the files can be anywhere on your disk (where you saved them from your browser or your mail, or on a network share) and their management if out of Gimp's scope (but I agree that the default directory in the Gimp profile is a bad idea).
(*) and if you use my settings-cleaner thing, those with a name are never cleaned.