Let's say you increase the armor on frozen heart from 100 to 120, and similarly buff armor on randuin's and deadman's. Lethality builds will still work in laning phase for marksmen, but will absolutely suck once the bruisers or tanks come down.
No.
Lethality builds aren't really super powerful on ADCs right now, and for the few good ADCs who can build Lethality (basically just MF), increasing armor values on items means nothing because they aim to snowball a victory before most champions get significant armor items.
Saying that armor items need buffed because of Lethality implies that Lethality marksmen are currently shredding down tanks, and that simply isn't the case. Both of the other common ADC builds kill tanks at a ludicrously faster rate. Lethality builds are actually pretty hot garbage at dealing with tanks.
If you want ADCs nerfed, the way to do that would be to nerf ADCs, not buff tank items when tanks already take 0 damage from non-ADCs.
They pen 20 and frozen heart gives 100.
It's already amazing vs lethality? lol
Just getting a Warden's Mail practically counters 2 lethality items.
(I know 40 pen vs 40 armor meets equally but it's still better than negative armor)
Yeah let's buff tank armor values and not buff Last Whisper / Pen items.
Sure way to enforce a tank meta.
Leaves me wondering what problems we have right now concerning leathaility ADCs?
I mean.. MF exists... but besides that?
<s> Good idea OP, but I say let's make everything 300 armor and just kill all AD champions completely </s>
Bruisers: Wow, I really love not being able to damage tanks!
Boards: Buff tanks.
remind you that any fighter building 
will continue to allow Marksmen to build lethality without problem until black cleaver goes back to 20% over all armor pen and gets more ad on it for fighters to do damage with their spells not just debuff for adcs. and on top of that defensive items still need health on them. idk why an offensive mage item is one of the highest health value items in the game 
This man speaks truth.
Tanks sure are in a rough spot right now lol
If you want to buff tanks, give them more MR per level since their biggest threat is usually burst damage mages.
how about just make lethality items start at 40% base armor pen if you're ranged?
and then how about every single other AD champion in the game? buffing armor items means little to ADCs or champions who can build 
and the items it builds into and it actually affects more to those who cannot get through those defenses. Yes you are making ADCs make you kill slightly slower but at the cost of ruining the game for those ADs that cannot afford to build armor pen/lethality items
Won't do much for tanks who build so much armour lethality builds barely do anything already
But for bruisers this is definitely true! Though really I want to see buffs to squishies so they're not dead instantly (but still go down really fast) by lethality
You do realize that 
dumpster Marksmen right now? Why do you want to buff these characters?
