Right, which seems like it would work. Animation engineering is a finnicky, nit-picky process.
This is what I’m talking about doing, here.
I don’t know if this helps you or not but it might be an easier way. Transitions are just so finnicky I try to avoid them whenever possible. 
As far as the instant idle, I’d say turn down your character’s brake, so they’re forced to slow down to a stop instead of stopping on a dime, as acceleration is definitely affecting the movement. Paired with Blendspaces that should do it.