Instant Mobility

A lot of problems with recent champions seems to be instant mobility. By this, I mean mobility without cast times. For example, lets look at Tristana. One reason her W is balanced is because it has a 0.25 second cast time. Compare this to Ahri R, Pyke E, or Kaisa R(and many others). These forms of mobility have no cast time. This leads to an unfair gameplay experience because the enemy has no opportunity to react to the dash. I feel like these newer forms of mobility could be more balanced by adding cast times, but then buffing them in some other way.