Everything here about sums it up; don't skimp on servos! Although linkage geometry and just plain airframe failure (older version Funtanas) can cause flutter, the servo can also be where it starts, ie, sloppy servo gears, output arms, etc. If you do get the mechanical advantage right with a lower torque servo, chances are that you will not flutter, but you will instead have blowback and will likely not have enough throw for true 3D.

One example would be my 27% Edge. When I had a 120 oz. in. servo on the rudder, authority was marginal at best. If you let it come out of a torque roll in a slight K/E attitude, it was impossible to bring it back. Knife edge was marginal and it did not lock into rollers very well at all. That servo eventually stripped on takeoff (it was even metal gear) and I almost lost the plane to it. (I'm repairing the servo now to put it in something else)

But, once I installed a 180 oz. in. servo, it is a totally diffrent plane. It locks into K/E very well (except for the bad coupling), locks into any kind of roller very well, and will even pull off a double hammerhead. (Two consecutive stall turns)

So, the lesson learned is, do not skimp on servos; they do not have to be digital-although that is a big plus- just a good amount of torque and metal gear if you can.

Hope this helps,
Brandon