If you knew nothing about the line or characters? How is that a feasible argument? If you showed a person the characters and the vehicles they would see the similarities between them, the knights have their crests on their chests and if they were equipped with their weapons, which would only be fair imo, they would see the similarities there as well.
You created an impossible task, ask someone which characters the vehicles belong to without showing them the characters.
Like I said, the consistent predominant colors and aesthetic creates a visual cohesion, despite the cohesive aesthetics the vehicles manage to be considerably more visually distinct than you're admitting.
Ninjago and bionicle use color prominence to convey difference, specifically elements, nexo knights is a consistent technology, all the technology is the same, so it being visually cohesive conveys that while also adding to the knight theme.