Light is pretty cool,strong,but he couldn't be invincible.The Death Note was almost flawless,yet the mistakes were user-made.So even if he's a genius,a crime-fighter and a strategist,he must have a weakness.
In terms of comparation,I put Light near Lelouch,yet I think Lelouch is far more intelligent.As for strategy,I believe he's equal,or not too high from Light.The thing that separtes them,is however,humanity.Lelouch's purpose was to create a better world for his sister,while Light's purpose was to create a fair world for him.Lelouch's first mistake was
to let Villetta live in the first episode
.As for Light,his first mistake was to give some heads-up for the investigation team.
Both Lelouch and Light are great characters,of that 10% that know the world.Lelouch's action scope far-surpasses Light's in all terms,but so do the mistakes,which cost millions of lives.