Do you feel TLJ is to blame for Solo's failure?
Probably both yes and no. I don't know if the content of predecessors was particularly alienating, it was to some but probably not many, but the franchise over-exposure (fourth film in four years) definitely at least contributed to the film feeling like nothing special. IDK.
Personally I think Solo failed due to being an origin story that nobody asked for
Yeah, even for a prequel its events seemed particularly superfluous and uninteresting, Han's story seemed already pretty complete and his backstory not important or exciting, let alone epic.