Outside competitive play, I rarely see people picking for the situation.
People just recklessly pick whatever they feel like playing, rather than what we need.
The composition failures I see on a regular basis include, but are not limited to:
* Not having an actual carry, relying on an Ashe or Jhin to wipe the enemy.
* Having too much of one damage type.
* Having no CC.
* Having no tank.
* Having no engage.
* Having no disengage.
* Picking poor match ups.
* Drafting too many late game champs without somebody to carry them through to the late game.
* "All eggs in one basket".
* Picking your teams trump card early in the draft.
You get the point.
What's worse is that people make these egregious mistakes, lose, and then complain that "the game is imbalanced".
Bring a knife to a gunfight, you're gonna lose.