All instances I remember seeing were neglected, not updated running on lowest amount of resources. Everyone in company nagging how slo it is but no one wanted to share budget to improve it.
So for me that experiment „it will be better and cheaper building our own JIRA” was already done. It is going to be cost center that no one will want to throw money at.
It would be hard to do worse. A packet of crayons and a scrap of paper is better than JIRA.
Yes, you wouldn't get something near as complicatedas JIRA, but that would be a good thing! Look, it's enterprise software, so I'm sure there's somewhere that needs to have the overcomplicated permissions system otherwise contractors are going to steal everything that isn't bolted down, but most places I've been don't need, and thus don't use most of all of that crap. If the ticket can only go from planned to done by a certain group of users, backed by LDAP... let's just say, I'm not going to miss configuring which group gets which permissions system.
JIRA's the perfect example of disruption, too. Everyone's got their bespoke workflow, and JIRA has to be customizable to suit all of them. Bespoke software just doesn't have to the same way.