I kind of want a modern version of Trac. Trac is essentially a collection of integrations that just happen to have useful features.
There's no "coherency" to them.
Take for example the admin UI. When adding "Application Links" to link Jira and Confluence with each other, Jira has a nice tabbed interface allowing you to configure it easily, whereas in Confluence, you have to scroll down a long sidebar with dozens of options until you chance upon the required link. Had similar experiences configuring various other options at the filesystem level.
Jira configuration was more coherent, fault tolerant and failed gracefully. Confluence configuration on the other hand was messy in comparison.
Whoever thought it was a good idea to build a CI tool on a concept of information hiding is a monster who should be banished back to whatever eldritch plane they crawled out of.
You can’t have a coherent conversation with anyone about the functionality of Bamboo versus other CI tools because Bamboo is constantly lying to you about what is available. You don’t even know to ask other people for help with something because you don’t know if Bamboo can do it. So people use the ugliest kludges that their privilege level allows to get things done, creating an unmaintainable mess in the process.
You are right that it's difficult to replace the entire Atlassian suite. The thing about Atlassian is that when there's if there's a box to check on a feature list, they've made sure to check it. If you go around the office asking everyone what features they want, Atlassian is going to check all those boxes. That's pretty hard to compete with.