flutter is a sign of not enough spin on the disc. Which means you aren't getting good snap. Forehand does not involve arm strength; only wrist strength and snap. Throwing with your arm will apply OAT which is what you're doing. Most likely you are throwing too much with your arm and not getting the snap and rip you need.
If your throw doesn't feel effortless, then you are doing it wrong. Even if it means dropping 50-100ft of distance. Distance comes from the legs and core.