A recent report by the Boston Foundation said that 65 percent of arts donations went to two percent of the area’s cultural organizations – the ones with budgets of more than $20 million. This has led some to call for spreading the wealth among the rest of the arts organizations. But leaders of two of Boston’s largest arts groups say the portion of funding for major groups is right because they serve the widest audiences. “That chart doesn’t show audience served. That’s the number one point.”