League-of-legends – black list other players

You generally dont build a last whisper after the black cleaver because flat Armor Pen makes the % armor pen less effective.

Say they have 100 armor. Black cleaver removes 45 armor, then your masteries remove another 6, then your 10% armor pen from masteries plays in, leaving the person with 45 armor. 40% of 45 armor is only a 10% damage increase, if that. And thats coming into play if the person actually bought enough armor to put them at 100.

Generally another AD item will give you more speed or sustain while providing more than a 10% damage increase.

First of all, let's clarify the question. This situation will only happen during online tournaments. During offline LAN events, players have infinite RP and IP as well as every champion purchased. During online tournaments though, players use their standard LOL profiles. As a result, there is a decent chance that some summoners will be missing heroes. When that happens, a placeholder champion that never gets actual play like Eve is chosen instead and replaced with the intended hero later on.

As for why they don't just pick the heroes as soon as they are available? In the current meta, the top and middle lanes are solo lanes. Since solo lanes are 1v1 battles, having to face an enemy who counters you can be too much to overcome. As a result, teams try to pick these two lanes last, in order to avoid getting countered.