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I partially agree, OP, but I think you're missing an extremely important (arguably the most so) element: creativity. I'd say that's what truly makes Gamefreak great.
See, compare this fan-made angel and devil duo to the official angel and devil duo. You could argue that both have the same competency in design, but what truly makes Gamefreak's own design better is that yes, they stick to the theme, but they put their own twist on it rather than going with the obvious depictions (as seen above).
What makes Gamefreak great is that rather than being slaves to what "should" be, they forge their own identity. That's how they came into creation in the first place, and that's how it should stay.