Don't you think MR is really strong compared to armor? There's no problem when your team is full AD but it's almost a guaranteed loss when your team is full AP. Armor is hardly ever noticeable while a single MR item halves the magic damage taken. Not to mention there are much more anti-armor items/abilities/runes compared to anti-MR items/abilities/runes.
BlueBilberry1 votesI wouldn't object to some of the starting armor and MR changes being reverted. But that's apparently not going to happen til the end of the season.
aaaustindestroy11 votesWell part of that is because almost always AD is more DPS-oriented and AP is burst-oriented, with the exception of probably Aurelion Sol. It's harder to itemize against DPS, but we don't have too much in that category.
HP Crookshanks1 votes
Most these champions are not burst oriented and all of them have high DPS like 
but still they can't kill a tank with 
without running out of mana.
are burst oriented but they can easly kill a tank with 3 armor items.
aaaustindestroy11 votesOut of your ENTIRE list, only Azir, Teemo, and Kayle are oriented around DPS. Every single other champion is pure burst damage, unless Corki builds AD. Because all of those mages are burst-oriented, of COURSE they're going to have trouble fighting a tank with pure MR. And even then, even if THEY can't kill someone, that doesn't mean that the rest of their team isn't going to be able to. Also, very few of those champions have high DPS, unless they're centered around DPS or are Heimerdinger.
In your AD list, Pyke does not deal damage on his own unless he is insanely fed, and even then he's not going to do anything to a tank. Hell, he has trouble against squishies a lot of the time. Pyke DOES NOT deal damage.
Jhin is DPS-Burst, and he's a special case. And he does not deal high enough damage, unless he has lethality and armor penetration, to kill a tank quickly.
Kayn only deals burst damage when he's in Shadow form, otherwise he is a bruiser and is built off sustain. Even when he's in Shadow form, he can't do much to a tank unless he's fed. Kha'Zix, Lee'Sin, Miss Fortune, Nocturne, Pantheon, Rengar, Shaco, Talon, Wukong, and Zed all have to be fed to a ridiculous level to be able to kill a tank on their own in the time that you're suggesting.
Every single one of those AD champions also build Lethality instead of just straight up AD. They're built to deal high damage to squishies and have trouble against tanks, and they DO. They have a lot of trouble killing tanks, unless, again, they're fed.