I am talking about the items only.
Since getting 3 of them seems to be a large part of the issue.
Having 30 to 35 from an item and masteries is not so much the issue.
It is when someone is able to get 80+ lethality on top of a LW a nd black cleaveritem resulting in ignoring often times 70%+ of a tanks total armor and doing true damage to squishes.
basic example of how the calculation works from my understanding (I might get something out of order since I am a bit rusty on when black cleaver is applied.)
Armor is 100/(100 + base armor + bonus armor) and 1 armor is an effective 1% more of your max health.
armor penetration and reduction is as follows 100/ (((base armor*(1-armor penetration)- flat armor reduction)+((bonus armor *.55 for LW item *1(-% armor reduction)-flat armor reduction)))-lethality)
So a tank with 90 base armor and 160 bonus armor armor would have 100/(100+90+160) = .2857 of damage taken. in other words this tanke has effective 3.5 multiplyer on it's health pool.
Against a enemy with 60 lethality a LW item and a black cleaver fully stacked from another ally they will have 100/(100 + (90*(1-.3)+160*.55*(1-.3))-60)= 100/(100+ 63 + 61.6 - 60)= 100 /(100+64.6) = .607 of damage taken. This tank only has a 1.646 multiplyer on it's effective health.
In this example
It is more a case of all the armor penetration easily works together that is proving to be the problem and since games are decided faster on average the nthey use to be crit is not evne really mentioned due to this being a more optimal early game damage option. It is a case of synergy being to fast and easy to get.
While Crit has a potential to outscale these armor pen builds it requires more items overall.