> For example, some apparently 10x engineers were only so because they were allowed to only work on interesting, relatively easy early stage work. The difficult, fiddly work of mopping up the awkward corners was left to other engineers, who were considered 'slow'.

I am someone who loves mopping up the awkward corner cases. For me, this is the most fun part of coding. I think the early design and infrastructure work is actually pretty challenging work. The decisions made at this stage pay dividends later on, in ease of debugging, api goodness, future expendability, etc. I prefer collaborating with senior engineers who are strong and relatively fast with that, and then I help clean-up to facilitate their speed. If everyone is on-board, I am not sure what is wrong with this arrangement.