Absolutely NOT. Quite the opposite I think. Using Flickr now pexels, stocksnap, unsplash etc.. will be able to cherrypick the best and highest quality photos from thousands useless on flickr.
The main reason I am using unslplash.com and other sites is the quality of photos. The other day I tried to use a CC photo from flickr I've spent most of my time just searching for a good quality photo.
Right now http://www.flickr.com/creativecommons (where I usually head to look for creative commons photos) lists zero public domain images.