My Brother is a Mechanic for Ford and i asked him if they were in fact having issues with the MKZ as a hot spot, he said no, but did add the biggest issue he does see with Sync is customers inability to pair their phone directly.
Have you gone to the dealer and had a mechanic sit with you to set up your phone? I would highly suggest this, not some stuffy sales men, they aare completely ignorant. Ask for a tech to have a look at your Syna, it will take them 5 minutes and is much more rewarding than watching a salesman fumble his way through
good luck