Darius will be fine with the buff he is receiving 5.7 and a movespeed buff to 345
Honestly speaking, the buff to his ult in 5.7 is an amazing buff to his already shitty late game and will make him much better to use, you can split push with Darius/farm to 16 and become a huge threat once you're 16 as your ult will fully refresh so the enemy HAS to send more than 1-2 people, giving your team more time for objective control.
The base move speed buff is simple, though he gains move speed with his passive, getting to his enemies is the PROBLEM, he's too slow to reach them.