the fact that BC, LW and Lethality work perfectally together is why tanks are seen as weak.
The damage is still decent on BC. The 400 health is something both assassin and Marksmen can make use of.
The 30% armor reduction makes both LW and lethality more effective.
Would it be that crazy making it so that if someone buys BC they can not buy LW/Lethality and vice versa. The synergy of armor pen/reduction in the game is a huge part of why people say tanks are weak.
If a tank could reduce bonus AD by 25% people would be up in arms. But being able to ignore 60% of a tanks armor is seen as perfectly fine?
You build BC as a middle ground item that reduces total armor by up to 30%
You build Leathlity to target squishes.
You build LW to deal with high armor tanks.
They all have their reasoning for beign built but they should not work together like they do.
Make players have to build to deal with problems. Not build the same thing and be most effective regardless of the enemy.
They would be fine on their own for their intended uses but they do not have down sides when combined.
Perhaps it is mainly the existence of Black Cleaver being all around to accessible that is the problem. If you build AD and deal physical damage you can basically always justify it and it benefits everyone on your team who deals physical damage. Make it only auto attacks again for the armor reduction and it will be less ideal.
on illaoi namely for the purpose of the huge aoe grievous wounds and to help crush enemy frontliners faster