So then I conclude that this version of sortition will shift the political power now held by experienced politicians onto experienced public servants (in addition to the power they already have).
I am not sure if this would be worse, but it would be quite a different political power structure.
Consider how well jury service (doesn't) work. A highly trained class of influencers can game the system towards their preferred choice of outcome using arguments and techniques that are knowingly manipulative.
You'd soon end up with an oligarchy disguised as a civil service. Representatives would come and go, the civil service would remain and "guide" them.
The real power would continue to be lobby influence - and very likely explicit corruption of both civil servants and representatives.
I am not sure if this would be worse, but it would be quite a different political power structure.