Cmon... after hearing about the new lore, you think a non-magical warrior like 
who throws axes could ever take on 
, who is an unkillable lord of Noxus long ago who is powerful enough to control an entire island through force of will?
Well Morde does have a weakness his skeleton it's a pretty damning kryptonite if you ask me. also we don't know too much about draven's abilities pass his skill with axes and legendary narcissism his fight with the knight proved that human technology was able to be affected by his magic should be reasonable to assume that you draven's axes has A similar ability due to a long lasting conflict with damacia and not wanting to be out done.
On another note Morde donesnt seem to control the will of the island it never directly says that just because the island is amassing souls that they serve him also we don't know to what extent Mordes domain was so I don't think you can reasonably call him the ro I don't think you can reasonably call him a old noxian leader as he calls them upstarts
Its the league of what more needs to be said?
Now do you see the reason why they made lore and gameplay separate entities?
Pre-Retcon the Fields of Justice had a magical aura that both returned the champions to their basic abilities (Thus why you have to gain levels again in each new match) and sort of leveled the playing field. Outside the fields, anything goes.
Post-retcon, the lore and gameplay are separated so, uh... don't worry too much about it.
Morde was never the king of Noxus, he was king of a kingdom that included that land that is now referred to as Noxus. It's like saying Ur-Nammu was the king of Iraq. He was the king of Mesopotamia, which happens to have included the area that is now referred to as Iraq.
To answer your question, champions aren't balanced lore-wise. That's why 'Who's the strongest' discussions tend to come up so much, and why the lore geeks among us love debating who could kick whose ass in a fight.
Well the league itself balances out the power of the champions, so it's more like making magical constructs made in the image of said champions that fight, hence why things like blinding Lee Sin and Talon bleeding Blitzcrank works. Also, Mordekaiser wasn't a lord of Noxus, he was a sort of god-king of the past that ruled over a vast territory that covered a lot more than just Noxus or Demacia.
Maybe even most of Valoran in fact, and he couldn't be permanently killed, only defeated for a time and his resurrection halted. His primary fortress was where Noxus's capital was founded, essentially making him an unintentional founder of Noxus itself, and he wants his citadel back. It's also never stated if he controls the island, it's just hinted that Mordekaiser may have potential influence over the Black Mist and the champions empowered by it because he is immune to it's mental influence while being still physically empowered by it.
Honestly, if anyone had the power to direct the Black Mist, it would be him. It might explain why the Black Mist hasn't just randomly tried to take over everything, and seems almost methodical in how it tries to invade, like how it chooses right after Gangplank supposedly falls to invade Bilgewater, if Mordekaiser is directing the Black Mist and taking his time in how he expands his empire, this would be a good indicator.
