Great kick & punt returners have:
1) Great vision
2) Some wiggle
3) Great speed
4) A knack for running in the open field
5) Great blockers & a solid special teams coach
6) Dependable hands
Hester wasn't the fastest guy on the planet but his vision, knack for open field running and acceleration made him one of the best return men of all time. Phillip Buchanon wasn't quite as smooth as Hester but boy was he awesome as a returner.
Berrios was a great Cane and a safe choice but IMHO called for fair catches a little too often. He also didn't have elite speed.
Lamar Miller had excellent speed but didn't have the vision & wiggle that guys like Hester had. He was more of a straight line runner (as a returner).
Mostly, we've been missing elite speed at the position. Also, our special teams coaching hasn't been stellar for a while. Even guys like Hester need highly competent blockers to be effective. We need stronger personnel groupings on ST this year.
We used to suffocate opponents with speed at every position. Elite top end speed has been missing at the WR & returner positions for a while now. We need to get back to that.