More qualification might also translate into doing a job less well. Sometimes what’s important is prompt response, staying on script, getting many jobs done. A deeper understanding could mean you’re more likely to be bored by the tedium of the more shallow role, more likely to spend too much time on an individual task, more likely to address a concern completely rather than adequately or quickly
For example, I am “overqualified” for many IT help desk roles and you bet I’d be slower than people that are good at the role. I’d be driven crazy by the repetitiveness and by stupid human tricks. At the end of my probation I’d be fired because while I answered that one customer in depth, my responsiveness metrics would be shit, I’d have addressed fewer than expected tickets, and I’d be dying to escape. Kudos to all of you who can do a better job than I.