Okay, I've been playing since s1, even though not all the time. For a long time I was convinced that s8 was the worst season since leagues beginning, and so literally anyone I know was. But you don't give up, don't you. This is what you have done (It's latest patch). Late game ADC (4+ items, ergo top dps in game) 1v1 Tank. I was literally laughing during that fight. No wonder pro players are hating league, making youtube videos about how bad league is and even leaving game last two years (Or claiming they stay just because they are addicted).
And it is so easy to understand basics how stategic game like moba should work.
1. Pretty simple formula, the more tanky champ is (or builds), the less dmg it has.
2. Top dps are always adcs (not only in late) and mages, for the price of being very squishy.
3. Assassins CAN oneshot those quishies, but ONLY in case they hit all their abilities (so not ik with zed on just e + one aa). Last two years those can do 2x-3x max hp of adcon full combo, so lower dmg cca to 1/3.
4. Tanks are in game for soaking dmg, but not for doing it + they can use cc.
5. Bruisers/fighters are somewhere on half the way, so not so tanky, but also never (!) with so much dmg as squishies. They use advantages of both.
That's pretty much it. You need to be able to place all the champ on this triangle, are you, riot?
Btw, that's the reason why top dps in game should always be Kog'Maw (Even though he can be out of meta for other resons).