Atlassian does not provide particularly good guidance on how to get their tools to perform well. The first big issue for any moderately busy system is that you need to dedicate huge gobs of heap memory (think 16G+) to the tool. After that, they suffer from poor schema design - there are tables that are literally missing indexes on commonly queried columns, and some columns that have delimited values embedded in them.

It's hard for me to imagine that atlassian would allow individual instances of jira/confluence/etc in their cloud versions to get nearly as much resources as you need to give them on-prem. The incentive would always be for them to try to minimize the amount of memory every instance gets, which does NOT maximize your individual performance. Shared resources will also make performance more variable and "noisy", making it more difficult to narrow down specific causes. It's hard for me to see how "Java" and "cloud" go together.