As a Voli main since season 2, I've played a lot of Voli top and jungle. Top lane is a lane where (at least at higher levels) how you play with your minion wave influences a lot of the lane's phase. Previously you could easily farm under turret by using E on your caster minions at full hp so you could last hit them (example here: https://www.youtube.com/watch?v=8f1cRMgjwEo) .
With the new knockback to his E, using it on a minion wave pushes it back so you can't last hit in time and messes up the timing on your wave. It's more of a nuisance than it is helpful to let E knockback minions, and since you guys want to support Voli in the top lane (seeing from the W change), you might want to look into this.