Did people forget that they should build armour/mr and hp against fed assassins?

Everytime the enemy assassin is fed, I tell my team to build more defensively than usual to not get 1 shot, but they say "he has lethality". However, armour is the most efficient against lethality stackers. gives 40 armour, if you have 60 armour and buy it, you will now have 100 armour, which is a 25% increase in survivability. If the enemy has 40 lethality, you originally have an effective 20 armour, but with a chain vest it becomes 60 armour, a 33.33% increase in survivability. If you deny the assassin the ability to 1 shot you, we can lock him down when he gets too greedy and get massive shutdown gold.