That’s not enough to represent large, complex projects. And sub-tasks are implemented in this weird, dystopian way that makes them unreasonably hard to work with in the system.

Agreed, the few times we've tried moving from separate linked tickets to sub-tasks have been disasters. It doesn't jive with any of the tooling in Jira to try to have tickets be like 'mini-Epics'.

You should check out the Structure add-on. Does unlimited hierarchies in a very intuitive way. Only for on-premise.

That is not enough! I regularly want to create sub tasks to subtasks, but it is not possible.

You could also link to other tickets or Epics with "relates to" or "blocked by".

And at that point why not Bugzilla?

Because "Oh, come on!". Just because you can implement any process in a list of text files and grep it does not mean you should. Jira has features that Bugzilla does not or needs plugins for. Should you just throw all of that away?

The complaint is that Jira's "features" are not much better. It's completely manual and only works if you strictly enforce conventions.

You also can have something bigger than epic - you could use Portfolio and create initiatives there.