I firmly believe the problem is snowballing. Let me elaborate:
There are too many opportunities to snowball at this point, and that leaves damage carries snowballing faster and faster, making these 1-shot builds more obtainable.
The bounties are downright crazy. I play WW, one trick, consistently. I often take an early game lead, but at some point the enemy team will finally snag a kill off me. This one kill can often be the tipping point in a game where we are decimating them. It is almost never the opposing jg that scores this kill. It is often the top, mid, or adc on their team that has gotten fed. This player that is already fed off picking on my team's weakest lane then gets bounty for me doing my early game job correctly up and down map. Worse, they then go on rampage collecting bounties up and down map. I would love to see the data on who actually collects bounties, it's rarely the champs that are down in level. Worse, the bounties are repetitive sometimes. I had a 1000g bounty the other day, dies, had a bounty again within 90 seconds, died and payed out that bounty, AND SOMEHOW CAME BACK TO LIFE AND STILL HAD A BOUNTY OF 450G????? This doesn't even take into account the fact that I'm playing early game champ, I'm not even overbuff, just appropriately buff for the game time and my champ.
Extra-reward systems like bounties will ALWAYS favor some champs or roles over others, they are impossible to manage/maintain fairly. Clearly they favor damage bursting champions in meta where people already complaining damage to high.
Take out bounties entirely, keep rewards and punishments as simple as possible, and then you don't have to repatch every other champion every other week...