Stated another way, proper design and technique in laying up a composite wing will be adequately stiff/strong and considerably lighter than the same size balsa veneered foam or all balsa. In other words, stronger/stiffer isn't really necessary

However, Bob Hunt and several other top CL guys routinely build 700 sq inch wings for CL models, finished in dope, that weigh in at 1 oz per 100 square inches. Not every one can do that and I'm not certain that ratio of weight to area will work in a free flying, heavier pattern model but it might. It will require open bays to achieve the weight but that's straight forward stuff