The "Myth" about "Sealing hinges" is that people believe that air flows through the small hinge gaps we use and that thereby causes flutter.

All too often the very first suggestion given to cure flutter is to "seal the hinges".

This is poor advice as it does not eliminate the resonance developing in the surface that causes flutter to begin with.

If sealing the hinges has any effect, it is due to the relatively minimal stiffening benefits it has, to help cure lateral movement along the entire hinged surface.

However having one part of the control surface moving out of plane with the other part ( e.g. a twisting force ) is rarely ever the cause of flutter that we see in our models and if it were a CF rod inserted in the surface is a much better solution.

Typically the entire surface tends to vibrate.

As you suggested a first line defense is to make sure all the linkages are tight, and if possible maybe even use multiple servos to hold the entire surface stiff.

Mass balancers are however used even in large aircraft to help reduce or eliminate flutter. Assuming lateral stiffness, they can indeed help eliminate flutter problems and can be so effective that they often appear to be a magical fix. I've used John's technique to make flutter "dissappear"

Ultimately the real "fix" is to fly the plane within the design parameters that it was built for.

Thick winged planes with large control surfaces are not designed to fly as fast as I often see people doing on their overpowered aircraft running at constant full power!