I think the story about the Libelle airbrakes is partly because the "open class" Libelle H-301 (an older model than the standard Libelle H-201, the higher number notwithstanding) had the airbrakes very far backwards on the wing to keep the laminarity of the airflow undisturbed. They were indeed rather ineffective. Those on the Standard Libelle are quite decent, if not overly powerful.

When Hänle was developing the Standard Libelle, the IGC rules for the standard class still specified terminal velocity airbrakes (speed lower than Vne in a vertical dive), and even if the Libelle airbrakes were not really that good, they still limited the velocity below Vne at a 45° dive. That was a point of contention, because the IGC accepted this without formally changing the rules. American manufacturers like the Schweizer brothers felt cheated because they had indeed developed - at great cost - terminal velocity airbrakes conforming to the rules for their standard gliders.