In other words, the Oda clan was already not under Nobunaga's direct control, therefore, if Nobunaga himself had a huge military force, it would have had a harmful influence on the organization (It was acceptable that Nobutada had a large military force).
つまり織田家はすでに信長の直接指揮から外れているため、信長自らが巨大な兵力をもつことは組織としての弊害が大きいといえる（信忠が大兵力をもつのであれば問題ない）。