Are delta patches still viable given the current sizes of games? I'm not sure if this is the state of the art, but according to https://www.daemonology.net/bsdiff/, bspatch would require more memory than most systems can offer.
I'd expect the patch generation to be memory hungry, not the patch aplication, which should be only data and offsets. If it uses maximum compression it might generate a huge data dictionary, but since it has to be distributed too, that would be contraproducent to patch size.