First, make sure you're saving over the first preset in the group of settings, like for the sharpness setting, you'll need to click on the "Image" button, and then save over the first preset. Second, the default preset only gets applied to new videos, because old videos already have their own settings saved. If you've already loaded a bunch of videos into the media library without the settings you want, you can click on "Media Library" in the left side panel, then delete the media source to remove the all the saved videos settings for the source.