Well, I don't know—in what way is the plot terrible? I haven't played Might and Magic, only Heroes. Yes, I prefer the campaigns of the second game over those of the third. But the plot is very sharp and clear; it's just that sometimes you actually have to read what they write. They say if you read the plot, it becomes understandable—you should check for yourself. Heroes 5 is only the pinnacle because of its name. Personally, I found nothing supernatural about them. The pinnacle is Civilization, if we're coming to that.
The thing is simply that pop culture always sells better than serious things.
In the third and fourth games, the spirit of the series is at its peak. Every artifact has its own destiny; every hero has their own story. How happy I was to see Sandro in the fourth game after seeing him in all previous parts.
And now the fifth one is resting on the laurels of the brand.
You'll see, even if Fallout 3 is ruined beyond belief (which will most likely happen), it will still be at the top of the sales ratings. The brand is a great power.