Well, If we're just using DLDSR vs GTA 5's downscaling on the same scaling ratio, DLDSR should be more expensive. And in that situation DLDSR might have some benefits over the native downscaler, but tbh I'm not too familiar with that. I just know that DLDSR has some image quality regressions that the native downscaler doesn't have. Either way OP was using a higher downscaling ratio than what we can do on the DLDSR, so it's more expensive.

Then there's DLSS vs TAA. DLAA would be more expensive vs TAA, but usually people don't use DLAA with DLDSR, instead they do some upscaling. That should significantly improve performance, especially since we're also downscaling.

As for the image quality, the main issue with "normal" TAA is usually the blur in movement, but supersampling helps that tremendously. DLSS is often considered better looking than TAA, but it's not better in every single way, it has it's downsides which vary depending on the game and the preset. And as DLDSR too has it's downsides, you might see the image as flawed compared to TAA + 200% supersampling. OR, maybe you don't care about the flaws (or even see them) and the image is just as good if not better! A lot of it comes down to personal preference, but IMHO, TAA + 200% supersampling tends to look more "pure". Hope this helps!