The thick trailing edge has two properties,(just my thoughts)

As stated above, it reduces the sensitivity of the rudder around neutral but does not reduces the effectiveness, this comes from full scale aviation, Cessna Citations have this, but they added a "T" to the trailing edge on the lower portion of it, or in some Bombardier jets the trialing edge is about 3/4".

The other is there is a small cavitation produced when the T.E. is thick enough, and this small vacuum tends to try to suck the airplane back thus reducing its speed.

Regards