Running is not a pendulum movement. The arms can and often move like a pendulum but the feet don't.
I don't like your idea of easing in and out off your key frames and I don't agree with the logic you give for it.
The logic that the viewer needs to be able to easily follow the animation and how you convince the viewer with anticipation I agree on but we have very different views on how this is archived.
I don't think I do "even" or "linear" animations. The Professor has linear foot movement because I can't pick his foot up any higher but the running woman (tom boy) picks up her foot slowly and lands it quickly.
I know what anticipation is in animation and I could add extra anticipation to the step of the run but I see no need for it because there is no need to convince the viewer that the the runner will take another set of steps forward every cycle.
With your animation style I am wondering if there's even GRAVITY in effect in your gameworld... isn't this a bigger gameplay problem than a few pixels worth of glide? Have you checked to see if the glide is even visible in fast movement?
Yes I have and it's highly noticeable and increasingly annoying the slower the character moves. I also run the game at twice the size it's shown here which makes it even more visible.