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To improve the sustainability of air travel, alternative aircraft and propulsion concepts are urgently required. Hybrid electric approaches have been discussed in the literature and are understood to offer benefits in emissions and fuel burn. For turboprop propulsion on regional aircraft however, contradicting estimates have been reported, ranging from a 30% fuel burn reduction to minimal benefit. The objective of this paper is to investigate if and how engineering assumptions and modeling fidelity differ between these studies, and to put the different findings in context. The analysis is based on physics-based modeling and simulation as well as empirical weight regressions proposed by authors of previous studies. The modeled domains include the gas turbine propulsion and the electric machine. Previous results are expanded across typical ranges of power levels. It was found that a central concept of operations (“downsizing the core”) could be conducted along at least two different directions, called conventional and constant power scaling. Other hybrid electric power train components than the gas turbine, in particular the electric machine, were often represented with less detail and mainly differed in engineering assumptions related to component efficiency and mass. A system simulation was conceived to predict and quantify the corresponding trends in fuel consumption and efficiency. From the results, the impact of conventional and constant power scaling of the gas turbine can be quantified. With one notable exception, most gas turbine engineering assumptions can be correlated successfully against these results. The most aggressive prediction of fuel burn reduction using parallel hybrid turboprops does not align with the correlated turboprop assumptions. For the electric machine, engineering assumptions in all considered references align with the predicted ranges.