Damage and lifesteal is getting absurd.

I was just in a game as Mordekaiser and the enemy team had a Master Yi and a Vayne so I built a thornmail, sunfire cape (just for the synergy with morde's passive plus a bit more armor), Rylai's, Liandry's, Ninja tabi, and my last item was gonna be a Gunblade for the active plus sustain.

Needless to say I was by no means squishy, I had a lot of armor and decent damage with a good amount of HP. Morde does quite a lot of damage and I was a pretty beefy boy. Me and master Yi run into eachother, we were both full HP and we had all cd's up. I ulted him for the bonus stats, he ulted me and literally just right-clicked me and did nothing else, he used E, never Q'd, didn't smite me for the bonus damage, nothing. I used all my abilities and he was in my passive the entire time, taking damage from sunfire and thornmail, and everything.

I died in like 3 seconds and he came out of that fight at FULL HP, not he came out hurt and healed with W, no he came out full hp the second I died without using W at all.

I had thornmail which applies grievous wounds so his healing should have been massively reduced, I did enough damage to kill their vayne pretty damn fast, I could chunk 1/3 of her HP with a single Q. Yi was able to outheal my damage from his lifesteal alone THROUGH grievous wounds and all my armor and the only MR item he had was a Wit's End, while simultaneously shredding through my armor and HP like butter by literally just standing still and auto attacking. HOW IS THIS CONSIDERED BALANCED?