Hiya
I think you are not quite understanding the concept. I will try and explain it another way.
Firstly no the GHL is not deficient, it has adequate leak protection based on water level of your system which is by far the most direct way of knowing if you have a leak. Yes i agree you can also use a moisture sensor, but that is only good if the leak is in the area that the senor is placed. this is why water level is far superior way of warning of leaks.
Water level dropping is the fastest and most direct way of detecting a leak in any scenario.
So to explain further, set level 3 to leak detection, then set a time period that you wish the alarm to be activated, this then stops false alarms by wave action or other similar things. Now if the water level drops over the set period of time lets say 2 minutes, the alarm will sound
If you then set up auto top off and provide that with a maximum on time for example 1 minute you do not run the risk of increasing the flood by water pouring in through your top off as the ATO tries to play catch up as the ATO will trip off 1 minute prior to the leak detection, furthermore you can set an alarm to this also giving you further warning of a leak.
As i said previous evaporation does not have an effect water would not evaporate to the time line that the leak detection was employed.
So you see by employing Leak detection by sump sensor you have THE fastest response alarm possible where as a moisture sensor is only accurate if the leak is present at the place of the leak or there abouts.
profiLux has one of THE most advanced level controls on the market, I hope you can see from this example there is no difficiency and why water sensors are favoured over external moisture sensors.