I agree. The way I see a development team leader is that the person should be thinking about projects alignment with company direction, improving development processes, delegating tasks, stacks (current and future) and the most important to me is the growth of your team members; 1:1 discussions, mentoring, career mapping. I don't see how the leader would still have time to do anything else, especially coding.
I understand that the willingness to get hands-on is still there; if it could be done faster by you or if the project would finish sooner, why not, right? However, letting yourself involved is (in my opinion) hurting your team members more than helping them. They won't get the experience or knowledge that you have, and you might have overlooked some areas in your own role since you spent the time doing what they're supposed to do instead.
If the knowledge gap is the problem, I would say do a pair programming so that the knowledge is sort of transferred. The next time similar thing happen, you don't have to do anything, they'll do it instead. If a company relies on the leaders doing too much and it still didn't work out, that could be a sign of a 'management smell' in my opinion. Either there's a resource problem or they're not delegating that much.
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