So this just happened

Tl:dr Nerf Gunblade and snowball isn't unstoppable.

So I was playing mid Ekko and took 2 towershots trying to kill Kassadin. Thanks to that I lost lane pretty hard while the other lanes were more or less holding their own. I got killed 4 times, was 1.5 levels behind and the enemy team started to siege... Unfortunately for them, I'd completed and . They couldn't kill me quickly enough, so I could freely jump in, proc my passive and then either stun them or ult out. Thanks to my superior waveclear and the sustain that offered, I could play as aggressively as I wanted. I ended up with most damage dealt and taken, my healing only outdone by Soraka. That's not to say that the enemy team didn't screw up monumentally. Their carries' builds were universally terrible.

Buuuut I think it's fair to say that not every game is decided in the first 5-10 minutes. Few people are gonna play perfectly and if you wait for slip-ups and abuse your item spikes (which are very strong right now), you'll always have a chance.