pattern_is_full,
Great summary!
Lomapaseo,
The expansion of the hot flowpath gas passing through the HP turbine and then entering and passing through the LPT pretty much sets blade hub to tip size of the LPT. The trend is towards higher LPT temperature capability, higher stage loading, fewer airfoils and fewer stages, but that is not always possible to achieve. Higher bypass ratios, i.e. larger diameter fans, require more LPT stages to fully extract the energy from the flow path gas. Aerodynamic limitations prevent a one stage LPT from consideration in a high performance LPT that drives a high bypass fan and booster.