I suppose you could enable the settings:
Preferences > General > Skip transform when placing
- Basically makes it so that when you mass import files Photoshop doesn't ask you to apply a Free Transform after every single image.
Preferences > General > Resize image during place
- "Determines whether to resize images to fit during place"
Preferences > General > Always create smart objects when placing
- Not necessary for this to work, but probably good to have.
...and with those settings drag the image files into your Photoshop document window. That's about as fast as it gets. It only downsizes to fit inside the document. If any files are smaller, they won't get upsized.
It doesn't take a whole lot of effort for anyone to test this, but because I got an immediate downvote, which made me realized that maybe I misunderstood what OP meant, here's a video.