Decrease the Base AP on Ludens & increase it's passive's damage.
Ludens is now experiencing the same problem Morells is - that most AP Champions are rushing it because it provides stats that are way too good in all aspects.
My suggestion is to Decrease the AP it gives, but increase the damage of it's passive. This means mages will only build ludens if they need the poke and not for all-in bursts. To compensate for these "changes", all-in items such as morells or rabadons should get a buff. This is the only way I can see AP itemizations actually getting fixed, other than a full rework for Rabadons.
Also, this isn't related but
is still very weak. There's like no reason to build it if the enemy has 1/2 tanks which is like 90% of game. MR makes this item completely useless to build, and such an expensive item shouldn't be that easy to counter.