hard meatballs or dumplings like matzo balls is directly tied to how much compression they receive... which is why so may commercially made meatballs are so tough - the machine squeezes them too much...

the mixture needs to be blended but not overworked... then take whatever amount you need for the size you want and lightly roll in your hands to shape them...

adding breadcrumbs or shredded bread will lighten them if they are allowed to soak up moisture prior to forming the balls and cooking... just like a boiled pudding or dumpling, outside moisture penetration requires along period of simmering to fully cook and that's tough on the meat because the natural fats get removed in the process... it's a balancing act... just like all the seasoning should be in the mix before cooking, they will only pick up a small amount of flavoring from the cooking water, sauce or gravy unless the cooking process is a long one ... though using a pressure cooker may have a different result - never used one for that