I personally think the heart of the game mode isn't something you enjoy.
Nexus Blitz is a fast-paced (~15 minutes) experimental mode designed for those of you seeking fresh ways to play League and low-pressure fun. It emphasizes exciting and surprising moments over intense competition, while still rewarding the skills you've learned from other League modes, like Summoner’s Rift.
In any case, I don't think the event is all that unfair. The only tweak I would make towards it would be to allow the Nexus to ignore unit collision so that teams can't purposely trap it. Gold leads are a thing in Nexus Blitz, unlike Ascension, so if the Nexus ignored everything and just went to a boxing match in the middle, the losing team would hardly even have a puncher's chance at that point (especially under the context that the OP presented).
If the game was more even, both Nexus would meet towards the center of the map anyways. In any case, just like in Summoner's Rift, one bad team fight late game is a death sentence.