I dont think Marksmen are the real issue in all cases (Graves still op). I think it is the items for ADCs being so much more cheaper and then there are those items that synergize too well.
This really benefits Marksmen over Tanks and APCs. Jaugernauts are also at a disadvantage, but still scale quite well with some of the new stuff that they seem to even outperform certain marksmen so freaking well.
I have seen players perform very, very well as melee champs. And I can even attest i have succeeded, it is annoying, really annoying, but can be done. You will be poked hard, will fall so behind on CS. You will be outgunned items wise for most of the laning phase, or the whole laning phase, but you could use the squishyness to your advantage. If you are a Fiora, you will scale great and then become virtually unkillable. If you are Mundo, the same. Rammus, the same. Trundle, you scale pretty well. And Malphite, that Level 6 all in (Funniest most weird thing ever). Shoot, even CC queen AD-ish Tanky Leona.
And if you complain about Blue Ez in Low Elo... then you are bad. Why? Virtually every low elo Blue Ez sucks, so they are easily beatable. SUPER EASY. They build wrong, they cant position well, they cant mechanically do much well. You should be fine against one.