yes. all that is true, but
the thing that needs to be accounted for also is:
unlike in the case with two different-weighted railroad engines, that have different mass but identical railways, identical speed and identical friction (drag is the same here)
two identical planes with different masses will have different AoA due to the fact that once needs more lift to keep AC at the same altitude if AC has more mass, than derivation of AoA = aerodynamic profile will be (probably) less efficient and this will create more profile drag (not induced, though). Since it creates more drag, it probably in some cases will be enough to counteract more momentum of heavier AC and thus the result will be the same = two aircraft will slowdown the same way.
everything depends upon particular coefficients and values. There is no general solution here to say that yes, it will slow down slower (or faster), I am assuming.