I’m not familiar with CH Solo Cello, so I’m not sure what you can do with it, but I can offer some observations from the perspective of having used various other libs, and playing the real thing as of a few months.
First thing I notice is that there are no legato transitions. Each new note has a sharp attack (marcato), as if played in a very distinct manner, from silence. While that’s possible to do to if desired, one would more likely play a phrase like that in a more flowing manner, with a mix of fingering (which results in an “instant” pitch change with minimal artifacts), string changes (much like what you have now, though the timbre differs slightly between the strings), and shifts/slides (“pitch bend” as the finger/hand moves, often in conjunction with fingering, so it will be “slide-jump,” “jump-slide,” or even “slide-jump-slide”).
The shift/slide thing is quite essential to the sound and feel of these instruments in legato passages, and it’s the one big features of legato patches in sample libraries. It pretty much has to be deep-sampled (as in, actual recordings of all possible intervals) and scripted for any chance of realistic results, so I don’t think there’s much point in trying to program it if it’s not supported by the library.