Well considering the fleet in "The Die Is Cast" arrived cloaked the use of FTL sensors for the defending planet is moot. The attacking fleet was already being fed false sensor info so FTL sensors or not would have made no difference.
So this example could instead show that even with FTL sensors, defending forces can feed it false information.
From a Trek POV, the FTL sensors just expands upon detection of FTL targets. They do have a limited range of a few light years for those carried on ships so its not like they know what is happening hundreds of LY away unless they had some giant stationary array. It's not as simplified as you'd like, but even our modern day radars are not cut and dry with the various RF bands and their effectiveness in specific ranges and weather conditions against specific materials.