How good Conqueror is on Mordekaiser?

I was thinking about that, especially since Mordekaiser doesn't really have good keystone options.

Conqueror gives AD, which doesn't seem like it is good for Morde, but his Q and his E in fact scale with AD. His Q actually scales harder with AD than AP (starting from rank 3). So it is indeed a good stat for Morde.

Then there is the 20% of damage against enemy champions being converted to true damage. It doesn't say that it only works with physical damage, so it should work with magic damage. Mordekaiser does almost entirely magic damage (even with his AD scaling spells). It is important to note that his ult deal magic damage based on a percentage of the enemy's maximum health. So in theory this rune would make him deal max health true damage in a similar way to Fiora and Vayne. Especially if you also get Liandry to add even more max health damage.

On other hand, Mordekaiser would have to stay in combat for 4 seconds with an enemy champion to activate this. This is not a problem early, but can be a problem later in the game, although by then, Mordekaiser will likely have enough defenses to survive. It also requires Morde to auto. He is going to auto anyway, however, due to his Q.

What do you think?