The point is that even if the stills show the fully rendered level of detail, that doesn't actually tell us how effective that level of detail will look in motion. What works in stills and what works in animation are two different matters. As I said, the low level of detail in Batman: TAS's designs looked bad to me in stills, but it looked far richer in motion. In animation, with the images in rapid motion, with less time to study each frame, a more impressionistic approach can work better. Collectively, all the different images and motions coming together in our minds contain richer information than a single frame. So what looks "not detailed enough" in a still frame can be just the right amount of detail in motion, because the motion itself adds so much.
And I don't really see any difference in detail or "grittiness," whatever that means, between the two design styles. The TCW design style was very simplified and marionettish, often to an ugly degree; if anything, this seems about equally detailed, just less angular and blocky, more naturalistic. TCW's art style seemed to draw on a mix of Genndy Tartakovsky's hyperstylization and Gerry Anderson's puppet characters, while this is more a 3D rendering of Ralph McQuarrie's design style.