I have looked at the AA K-UP fares and seen that al least UA/CO if not others offer the same. My option would be to buy one ticket ARN-LAX and DEN-ARN on BA as open jaw, and a one-way K-UP from LAX to DEN on AA. This is more expensive, and provide no flexibility compared to the Star option.
So my verdict is that value for money with stopover in the US, the Star offer is significantly better than the One World offer. Whilst I enjoy BA CW, I don’t think it worth 30-35% more than LX business class.