I’m having troubles imagining how more experienced eng could be slower than junior provided their code is reviewed and tested to the same standard. Unless the task is so soul crushingly rote that your senior is looking for another job rather than working on it ;)
The senior might spend more time doing PRs (juniors might not feel as comfortable), more time in meetings discussing new projects or architecting around arising problems. A junior is generally more enthusiastic so might voluntarily work longer hours to close of tickets, or just take fewer coffee breaks than a senior. A senior might also spend a portion of their time training juniors.
I’m not saying a senior engineer can’t be a prolific at closing off tickets as a junior, but more seniority means more responsibility and that often means less time writing code.
But there are also occasions when I might genuinely expect a senior to be slower. Like if they’re in their mid to late 30s and have young children who aren’t sleeping. People say you shouldn’t bring your home problems to work but the reality is that we are not robots and if you’re not sleeping at home then you’re performance at work will suffer. Whereas most 20-somethings have fewer commitments outside of work.
If we are talking really senior, like 60s, then a sad fact of reality is our mental faculties aren’t going to be as sharp as they were when we were in our 20s. So it might take an engineer a little longer to solve complex problems than someone fresh out of uni. Particularly if it’s an academic problem that one might have studied at uni but seldom need in your career.
So there are plenty of mitigating factors that might affect the throughput of a senior engineer. But that doesn’t matter but you hire them for their experience rather than their youthful motivation. And it’s also why it is important to have a balanced team of junior and seniors.
