We have more devs than that, and we spend way less than 1 FTE (or equivalent) per year on keeping it in good working order. Our biggest issue is when we want to do something that's not well-supported or hit bugs.
Don’t get me wrong, we are owned daily by Jenkins bugs. We just push as much as possible out of job config and into shared workflows & Makefiles, and treat Jenkins as a glorified cron with a web UI.