Don't dog on spark plugs too hard. You're right: they aren't complex. But they have to function in the kilohertz range, at more than a thousand degrees, in megapascal environments, under high voltage, for years. That makes minor quibbles of metallurgy and impedance take on an outsized importance. By the way, NGK all the way.

To diesel or not to diesel is a more complex issue than you think. All countries measure emissions differently and all countries tax fuel differently. German standards for diesel emissions are low and their diesel taxes are low. Thus, Germans buy a lot of diesels. American standards for diesel emissions are punishing and their diesel taxes are higher than petrol. Thus, Americans buy almost no diesels. I don't know what the standards are like in Japan, but they aren't selling a lot of cars to Germany. Also keep in mind: Japan has no oil reserves but their grid is (was) largely nuclear. Hydrogen becomes the way to go, because a hydrogen fuel cell is effectively a roundabout battery.

'member when the UK had a car industry? And how they lost it by producing abject pieces of shit? That was painful to watch, too, but it was also inevitable. And at least the British didn't hide their piece-of-shititude.