We use confluence and jira, an d for some reason it seems perfectly usable compared to others stories here. It's not a small organization either, so I wonder if it's some misconfiguration that's killing performance for others?
EDIT: Someone else in the comments suggested that the cloud version is slower than on-prem. This might account for things; if I've only seen complex on-prem and simple cloud, it might well be that simple on-prem can be fast. But... that's still concluding that Atlassian themselves can't make their own software performant, so it's not exactly a redeeming quality.
Atlassian tools are decent enough, and mostly usable is how I'd describe them. I'd take anything else though, even Rally.
I've been using Jira Cloud off and on at various startups and it always had its slow moments. At my most recent startup, it's been working very well with no slowness thay I'm aware of (knocks on wood), and that includes all of the stuff I do directly via API.