So, seriously can we STOP pretending that 20 more mana on a skill you max first and use CONSTANTLY isn't a substantial hit? Because it most certainly is, sure its not going to fix the bigger problem here (Darius' absurdly strong heal) but its still definitely a pretty decent nerf.
And if Darius is somehow landing 3 man-Q's every single time he's using it, you deserve to lose (mostly because your team is positioning like idiots).
That said, Fairly certain Morde is worse off now, notably because his solo lane healing doesn't outdo the health cost on the ability. He really just needs to be reworked from the ground up, so he can actually be balanced in a solo lane.