When you're at full build as a tank

i think it's some kind of skin ointment

NO WORRY I AM GOOD BLITZCRANK I BRING FRONT LINE TO YOU

Never heard of it.

Fixed it

my bad. Shows how much I jungle. XD

Thats what armor pen is for, a single randuins will not make a champion deal no physical damage. Itemization has always been the most reliable way to counter a champion, and for vayne, the only counter there is is exhaust/wither combo from nasus. Her only valid counterplay is to make sure she can't attack, which is the generic counter for those without legitimate weaknesses. Playing alistar and having the bitch completely ignore your ultimate is anti-fun, at least with cho'gath and darius they had to use an ultimate to counter an ultimate.

Thing is it really isn't as good of sustain as you think in the late game. Let's look at the biggest tank jungler right now, Sej, vs someone like a Jinx in full build.

Jinx will do more damage, but Jinx is also going to have to burn through a significant amount of HP and armor to kill the Sej, around 300 armor and 4-5k HP. Even with a Last Whisper and an Armor Pen rune page you are looking at Sej having around 200 armor still, which reduces your damage by around 63%. Now say you have enough life steal to counter Thornmail, you will still be taking Gromp buff which at 4k HP would be 210 HP over 3 seconds or 70 damage per second 34 from Cinderhulk, so 104 total so far. Now to add her abilities, assuming no AP to make it simple...

260 from her Q 180 from her E 350 from her R 120 from the AA part of her W also at max level Sej has 111.4 AD baseline so 231.4 40+3% of your max HP per second for 4 seconds, or 160+12% of your max HP.

Jinx baseline has 1856 HP at level 18, with masteries I'm gonna say around 2k at max level. For Sej's entire kit over 4 seconds, assuming she gets zero AAs, she is looking at dealing 1957.4 damage to Jinx.

Jinx with a BT, BoTRK, Last Whisper, and IE will have around 329 AD and if she is using Fishbones she gets a 10% bonus on top of that so 362. Going to be extremely generous and say every atk Jinx does to Sej is a crit which would put them doing 904.75 before armor. With Sej's roughly 205 armor after Jinx's armor pen, including your armor pen rune page, Sej will reduce that by around 60% meaning she cuts 542.85 damage off of those crits leaving Sej taking 362 damage, effectively nullifying Jinx's crits all together. With sej at 4k HP Jinx is gonna need roughly 11 AAs to kill her on her own, although she gets some leeway because of the BoTRK active.

Are you starting to see how the fight favors the tanks far more than the ADCs? With a 1.5 atk speed, which is generous for Jinx using Fishbones, Jinx will need 7-8 seconds to kill Sej which is twice the time Sej needs to damn near kill her just off of staying close, not even factoring in the fact that Sej will more than likely get 2-3 AAs off shortening the time even more so. Right now full build goes to tanks in the 1v1, outside of the Kog/Vayne exceptions, if you assume equal skill/builds.