I know that feeling...... had a Tryndamere 1 hit me at full HP on Pyke yesterday while I was Eing him.
But..... it takes awhile for them to get to that point..... Can always try to pressure the game so hard once you have a lead that it never gets to that point.
Earlier today I 1v5'd a team so hard on Pyke I literally kept the other team dead 50% of the time and my ult was up about 40% of the active game, because they kept dying right before the renew duration expired. The other team never could get to the penetration state.
At that point it's all about picking your battles. Split pushing. Defending turrets. Hoping you have a mage or something to long range them.