BB and TDK are both older masters with different color timing and in places excessive DNR to remove the natural grain of 35mm--with neither resembling the original theatrical presentations in either digital or film--especially the film prints.
BB is in dire need of a remaster and despite my loathing of it, so does TDK. The IMAX scenes ideally would be at their original 1.44:1 ratio and then seamlessly switch back to 2.35:1 for the Panavision 35mm majority. But the 1.78 was a compromise to the usual "Joe Schmoe" video average who supposedly favor pan n' scan releases to lose letterboxing bars. (also the reason why nearly 100% of films are cropped to fit a 1.78 hdtv frame nowadays--but this practice goes ignored.) You still get the sense of a larger scope due to the increased resolution in both originating camera negative and pixels on your screen, but this is somewhat negated by cropping and then the DNR on top of that.
TDKR looks better being a modern transfer, but it has the same problem when coming down to aspect. That said the 35mm sequences look better on the BD than the IMAX 65mm print, because those were so nasty looking that they more closely resembled projecting a video onto your childhood bedroom wall. The flashback scenes taken from BB and TDK were especially bad and were filled with digital noise.
BB reminded me of the original Terminator BD in it's softness the the last time I watched it. It looked marginally better than the DVD but not anywhere close to the detail that the BD format is capable of.