I believe GP meant that not for closed cycle engines, but for all turbo-pump driven engines, which in USA mostly means open loop (gas generator) engines. In USA

I believe GP meant that not for closed cycle engines, but for all turbo-pump driven engines, which in USA mostly means open loop (gas generator) engines. In USA the tradition was to add complexity in form of gears and extra axes to get pumps running with more optimal speed, while in Russia (USSR) it was to reduce efficiency and gain in simplicity, robustness and mass.