Are you saying that "I" am saying a ToS gives the site owner the right to "carte blanche"?
I have the following in my ToS:
"7. Submission of Content on this Web Site
By providing any Content to our web site such as text, tutorials, reviews, previews, written articles, images, artwork;
(a) you agree to grant to us a perpetual worldwide, royalty-free, non-exclusive right and license to use, display, reproduce, modify, publish, archive, translate, and to create derivative projects such as tournaments, competitions and compilations, in whole or in part. Such agreement to the license will apply with respect to any form, media, technology known or later developed;
(b) you warrant and represent that you have all legal, moral, and other rights that may be necessary to grant us with the license set forth in this Section 7;
(c) you acknowledge and agree that we shall have the right to remove and or block any access to any "CONTENT" you provide by uploading, or add by means of text into our forums or in articles you submit, but not obligation to remove it only at our sole discretion."
That doesn't mean I am going to reproduce the content but by registering and creating an account the registered member(s) explicitly agree to our Terms of Service.
If you and I are on the same page that doesn't mean that what happened with the OP and the other party is justified by any ToS or even copyright. The other party, if this is the OP's database has stolen their property in this case their (database) regardless of who posted what on the OP's forum or site. This "can" be resolved by what I suggested the OP do with just a simple letter to beging with.
So yes, proving damages is going to be very difficult.