Lethality isn't the problem. And neither is tabi. Back in the day, ADCs use to make randouins as their last item to prevent assassins from killing them. The same thing with GA. The LCS is just showing how unimportant zerker greaves are with the other solid attack speed items, or caster based adcs (jihn, varus, lucian, mf). Tabis aren't the answer to assassins. Armor is.
Tabis are the answer to auto-attackers. Which riot has made intensely better by nerfing burst damage the 5% - 2.5% mastery in the offensive tree. Along with ghostblade's lethality and lethality as a stat instead of flat pen. This has been a slow scaling back of assassins. When all riot has to do is give AD's an item that gives both ARMOR and ATTACK DAMAGE or ATTACK SPEED. There's already an item in the game for ADs when faced with burst Mages (Hexdrinker), but there is no item in the game ADs to defend against burst assassins. The closest thing currently is frozen gauntlet, which is only useful on Ezreal and Urgot (maybe).
The lack of understanding of basic game mechanics in the community is outstanding.