For a champion that is required to position relatively forward where he needs to be able to soak a lot of damage, Morde is inexcusably squishy.
**Morde is one of the lowest HP champions in the game.**
So darius/garen/mordekaiser are the three 1 cost knights. Lets compare HP
Morde has 500/900/1800 **[35 armor]**
Garen has 600/1080/2160 ** [35 armor]**
Darius has 600/1080/2160 **[25 armor]**
**Even champions with lower armor stats have more HP**
Warwick (30 armor) 600/1080/2160
Might I add, he is also quite essential for any phantom composition.