True that, this isn't suitable program for that. This is better for hard-edge images.
For soft-edge images, you'll need to use XnConvert (free) to mass resize smooth images:
1. Get XnConvert: https://www.xnview.com/en/xnconvert/
2. Drag n drop you images into it.
3. In the 'Actions' tab, find the Add Actions>Image>Resize. Choose settings.
4. Check the 'Output' tab set up where to send the files, what format, etc.
5. Press 'Convert' button and it should be done.