To save following the link, the response reads:
Hope this helps you lot get back to normal quickerI found the problem. They made a separate folder that keeps all your saved info.
Go to %localappdata%\insurgency\Saved\SaveGames\, open up the Profile folder, copy ALL of the .JSON files from there and put them in the SteamProfile folder.
This will bring back your presets, keybinds and other settings.
If your class loadouts are still empty, open up Insurgency:Sandstorm properties in your Steam Library and disable the Steam Cloud temporarily.
Copy over the Theater.json like before, launch the game and check if they're there. After you're done, exit the game, enable Steam Cloud again and enjoy.
Thank you MAD_ST for finding this.