Yes of course rocketry is complicated. ITT we're discussing the specific question that parent raised: are a bunch of small-payload rockets more efficient than o

Yes of course rocketry is complicated. ITT we're discussing the specific question that parent raised: are a bunch of small-payload rockets more efficient than on big-payload rocket? We assume that actual engineers have done the work of designing rockets that actually reach orbit, whether small or large; that's why we assume equal velocities. Any particular orbit is characterized by a specific orbital energy. Tsiolkovsky certainly considers the effects of gravity; that's the point.