Honestly both theories seem daft one way or an other. you're suggesting 900p + blur filter before upscaling it to 1080p is crisper IQ apposed to supersampling from 1080p. the goal is to retain IQ not smear it up.
I wasn't talking about that at all. The two ideas were discussed discretely. I'm saying the idea of downsampling 1080p and then upsampling it again is stupid. You'd just stick with the 1080p original. If you intend to do that, then instead take 1080p and blur it. You'll get the same results (better, actually, although imperceptibly as we're talking about quality of small radius blur) for less effort.
If you're not going with the shrink-and-grow solution, then the actual sensible approach given the info we have is to render the game at 900p with AA and then upscale. Choice of blur filter is artistic. It can be used for 'AA' but I don't think that's the case here, nor what I was recommending.
When I see Ryse i don't see much smearing, but I do see the pointless back and forth rendering logic you're referring to with supersampling, but that's how it works.
What do you mean 'that's how it works'? No-one does that. You don't take a native resolution screen, shirnk it (unless you need the performance or something) and then grow it back to native. That doesn't introduce AA. That introduces blur, and it's quicker and easier to just blur.
If you're talking about Tekken 6, Namco are rendering 768p and supersampling for 720p output. It only gets upscaled again if you output to a 768p display - that's not a deliberate part of the output pipeline. Otherwise, for 720p Namco would be rendering 720p, shrinking to something like 600p, and upscaling to the TV. Which they don't do because that'd be crazy!
The uncrazy solution here - Ryse is rendered at 900p with AA just as normal, and upscaled just as normal, like every developer does when rendering sub-native.