I don't think the noseleg is inherently weak but it is effectively an undamped spring. Bang the nose down and it will bounce back up before coming down again. If it survives the first bump a bit of throttle will soften the next blow...... Lack of ability to land on the mains first and an instictive need to keep the weight off the noseleg (good practice for all trikes as you all know and do
) is what makes Grumman owners reluctant to let hirers take them into grass fields with any hint of undulations.