You base your champion pick based on the enemy team comp and take measures to avoid feeding snowball champions.
Did the enemy just pick zed? Diana and annie have always been solid vs champs that need to get close. How about taking unconventional mids like Garen, malph or cho? Or any other champs that is relatively durable and can push him into the turret. You better pick an adc who can build steraks or that has self peel, trist, corki and graves are always reliable. He
So QSS was nerfed? Better stick next to your support or ask if they can pick ali, blitz, or lulu.
Is Zed mia? Dont push into an enemy turret without a ward in your river and behind drag. This goes for all assassins.
This isnt a solo game, even in solo Q you need to work as a team and make smart choices so that the rest of your team doesnt suffer. If you give zed two kills bot while your mid laner is maybe roaming top, collecting blue, or coming from base then theyre likely going to have a hard time and now feed further.
Zeds annoying but hes no more unbearable than rengar, fizz, and diana. If he didnt have death mark how would he contribute to a fight other than throwing shurikens? Now that QSS is gone more champions can be balanced based on their overall potential to do damage. Warwick, malz, Trundle, and Vlad all come to mind, and now you no longer have to waste gold on an item that really doesnt provide much resistance against physical champs.
I don't even play zed, I suck with him, but I understand team dynamics and the difficulty with balancing over a hundred champs alongside items that can negate a large portion of their kit.