Regarding the low overall bitrate - these are DVB-C streams, and german cable network providers try to really squeeze the last bit out of their bandwith to broadcast some hundred useless home shopping channels.
Besides that they use a very dynamic implementation of VBR. Although the overall bitrate is somewhere around 6Mbit, during high motion scenes the peak bitrate is somewhere between 11 and 12Mbit.
Unfortunately I don’t have the technical setup to capture DVB-S streams of Sky, which would have a significantly higher bitrate.

I hope you still can use the streams for any kind of preservation.