After uninstalling from Steam you need to delete two CK2 folders; the user files under Documents, and the game files under Applications (use spoltight to find ck2.app if you can't find it otherwise). Only then should you reinstall everything from Steam.
I'm just confirming that I had this problem and this is basically the fix. For the benefit of the QA folk, this was my process.
1. Bought all the new DLC on Steam. Started the game, played for an hour wondering why the retinue tab wouldn't work.
2. Exited the game, noticed that the main menu stated it was patch 1.07, with the right checksum, but that it was advertising me to buy DLC. (I had already bought ALL the DLC). Noticed the Ruler Designer was also greyed out. Came to the conclusion my DLC must not be recognized.
3. Rebooted the entire system. Same problem.
4. Verified files via Steam, and ran it again. Same problem.
5. Uninstalled game via Steam, and then reinstalled it. Same problem.
6. Manually deleted the CK2 game directory, and then reinstalled it. Same problem.
7. Manually deleted the CK2 "My Documents" directory AND the CK2 game directory. Reinstalled it, PROBLEM FIXED!
The problem seems to be the \MyDocuments\ParadoxInteractive\CrusaderKingsII directory. Perhaps the dlc_signature file? I don't see anything else there that would affect the game configuration like that.