I find the strengths of the 7800 reminds me of the Odyssey2 also: lots of moving objects, but not as strong (as the contemporary competition) with the background elements or resolution.
Myself, I see the 7800 in similar class to the C=64/Atari 800, with the NES/SMS in a set a bit more visually capable.
The former three are mostly "modified four colour" systems at a lower resolution, and "modified two colour" system at their higher resolution.
The latter three are "modified four colour" and "modified sixteen colour" systems at closer to the higher resolutions. I think the SMS is definitely an evolution from the NES towards the PC-Engine.
(I will be the first to say I really don't know, but...) I think the 7800 was more of a cost correction/market image correction than an enormous step beyond the 5200.