Q sucks. Q gives damage but no utility, escapes, or aoe damage. Q may be more damage but you will die much faster with no utility. Only put 1 point in Q because all you want is the 8% health damage for executions.

E slows attack speed and movement speed. Put a malphite E on the ADC, get better ganks from jungler, win trades and deal AOE damage too the whole enemy team.

You want to slow. Build these items above to slow the ones you want to kill.

21/9/0 for damage and defense.

E doesn't have a great early game. Take these to get your early game.

Flash for escapes and plays. Ignite for damage and securing kills.

E for slows, W for sustain and Q for extra damage late game.

E is the reason Lee Sin is OP. Max E to abuse this.