When running a team you need to balance bus factor and performance.
On an average software team of perhaps 10 people, you will naturally have people develop expertise in a particular part of the codebase. One developer will be an expert in the frontend, another in the SQL queries, the next in the controllers, etc. What you want to avoid is a bus factor of 1. Some teams try to keep every developer knowledgeable in every area of the system, this is a waste. If you have to work on every part of the system you will not be able to master any single part. To get a bus factor of n by rotating developers through different parts of the system you give up the efficiency from letting a developer master a subsystem. My solution is that you should focus on getting a bus factor of 2 for each major subsystem. Have people focus on the two subsystems that they are interested in or are available and leave things there. Just try to avoid having two developers working on the same two subsystems. You are unlikely to have two developers get hit by the ‘bus’ at the same time.
Aim for a bus factor of 2 while trying to avoid a lot of overlap on subsystems, then leave things there.