Some random thoughts...

(I was a kid in the 80s and I played in arcades a lot. I think I could still tell in which arcade I played each game).

> There was an economic motivation for this difficulty, in getting more coins from players quicker, but Fujiwara would later insist that wasn’t the primary motivation and that they were meeting a demand from strong players for challenge.

Thats' not completely true. If it was that way, players would quickly grew fed up and stop playing. You need a balance between getting money out of people and people keep playing because they have fun.

I think one of the most efficient way to do that is having MOST of your players being suckers that keep pouring money, but allow a few to get very good at it, and play an inordinate amount of time with a single coin. That way the suckers will keep playing hoping to do the same. Most people would last 5 level in Bubble Bobble, but you had the occasional "genius" that would finish it.

Very difficult games like GnG were well regarded but not as played as others, as much as I can remember.

> Fujiwara later responded to a question about SNK’s Ikari and its resemblance to Commando by saying that was just how things were, although he was disappointed that they had got to release more sequels than him.

In the 80's there were not many game mechanics available []. I dare say that 90% of the games were either

vertical shoot 'em ups (think Galaxian) * horizontal shoot 'em ups (think Gradius) * beat 'em ups (think Double Dragon) * platform (think Mario) * to a lesser extent, racing games (think Outrun)

I think mostly due to HW limitations.

So if you are going to have a soldier going around killing people, of course it is going to resemble Command in some way. Doesn't mean they are the same, in the same way that Poker and Bridge are not the same despite using the same set of cards.

[*] There were some outliers, and some of them were great (Tron, Star Wars) but they more the exception that the rule.

Ghosts'n Goblins – “Worse danger is ahead”