Some incompetence is a known quantity, and when it is known it will not produce stress. The junior dev on the team might not know how to do something. The team leadership should already have priced that in, and have a plan to help them if need be. If the junior dev's incompetence is creating stress, the root cause is leadership incompetence.
The kind of incompetence that produces stress is incompetence that is too impolite to mention. It can't be addressed through "mentorship" or "working together" because that would call the legitimacy of the role and the person filling it into question. Engineering managers who don't understand engineering, product managers who don't understand the product, etc. The list is long, and examples are common. The organization is built around the assumption that these people can do things that they are unable to do. That mismatch is the origin of stress.
Investing time in the 1st kind of incompetence is a good investment because you will get a good return on your time invested. The junior dev with potential becomes the rock star. The 2nd kind of incompetence is often "Throwing good money after bad". These situations are not worth your time. There is unlikely to be an improvement, and you risk it backfiring especially if the problem is above you in the org chart.