You are suggesting that they should design a brand new upper stage to get the thing to put 50 kg into orbit, as an alternative launch platform for their 600 kg satellite? Instead of investing that engineering effort into finishing their New Glenn rocket which delivers 40,000 - 100,000 kg at a time to LEO?
Here's a possible (and apparently simulated) option: https://space.stackexchange.com/questions/51480/is-new-shepa...