I wonder if self-hosting is the performance difference. I have worked in projects with 15 years of history in Jira. And they were fine. It feels kind of slow but in reality it takes maybe three seconds to load any ticket.
But actual minutes to load stuff? That is insane and I can see where the loathing would come from.
A lot of anecdotes are possibly from some years ago where self-hosting JIRA meant a single server on-premise. You might not get a lot of resources and can be used by the entire organization. The server would be at or over capacity 90% of the time so things could take forever to load.
Self-hosted JIRA also opened up to lots of customisations and hacks, which often weren't performant.
With enough data it's possible - I remember a colleague going to a conference and chatting with some Atlassian people and they said their priority (this was probably 2016 or 2017) was getting Jira to be performant for companies with 500,000+ people. With enough users, labels, releases etc I can see Jira churning on something for minutes.
But actual minutes to load stuff? That is insane and I can see where the loathing would come from.