Probably not possible to describe. Jenkins is just tool, if used wrong it will bite to operators. Problem with jenkins is that it's takes time to setup workflow. You configure to run plugin-install-tool, JaaC, Jobdsl, Shared Libs, some credential store etc. But when it's up and running, oh boy, it's factory. I have run jenkins with 5k+ jobs. All auto gen, no manual interventions etc. Gitlab-CI (same as github actions) I like due opinionated approach. It makes things easier if setup is simple, but when you need exceptions or special cases, hack's begins.

But, yes, I have seen so many badly implemented jenkinses.