How to add counterplay to Darius W -> Q for immobile champions
Make his W only slow by half the total amount when moving towards him, that way you can more reasonably "dodge" the Q by moving into it since that was the intended counterplay.
This doesn't affect his ability to catch targets, since a target running away will probably not want to move closer to the person chasing them, but it does add more reasonable counterplay for immobile champions to duel Darius in lane.
I don't think Darius needs nerfs or anything, I'd be fine if he got some sort of compensation for this (really don't think he'd need it though), I just think this change needs to happen to make laning against him as an immobile champion more feasible.
Edit: after some thought I realize this only really matters very early on. It would be totally fine if this effect scaled down with rank or level (ie. 50/62.5/75/87.5/100% of slow amount when moving towards him)
. W slow makes it essentially impossible to dodge for these guys. Ironically, he does the best vs other juggernauts in the early levels. And by best I mean atrocious minion zoning you get 0 CS good.