Design doesn't care [much] about comptetive Standard.* MaRo's claim that vehicles worked best with other vehicles doesn't seem right, given that even Mardu Vehicles ended up only using one vehicle type.
Also, he didn't say that vehicles work well with other vehicles; he said that vehicle decks were all-in on vehicles (with cards like Depala and Veteran Motorist) or running none at all. They'd expected them to show up in non-vehicle decks here and there.
To be fair, plenty of non-vehicle decks ran vehicles, but only for the busted vehicles (Heart of Kiran and Copter) and as sideboard slots (Skysoveign and Aethersphere Harvester).