If I combine our three internal ticketing systems, we end up with something like 200k - 300k tickets, with maybe up to 5M comments on those in JIRA-Terms. If you throw a small-ish, decently configured postgres with 8GB - 16GB of memory at it, it'll keep most to all of that in memory at all times, indexes will be analyzed and fine-tuned to your specific dataset. It will answer queries very, very fast. Any cache in the application servers will also be primed with your data 24/7, speeding it up even further.

JIRA Cloud is most likely not an in-memory problem as a whole at a database layer, so it is at quite the disadvantage performance wise for a small customer.

(In case this turns into a SaaS-Hate-Thread: Yes our customers could have a faster system if they were on-prem. If they had the same experience and expertise running postgres as well as all the other necessary middlewares. And then we're not talking about non-functional operational requirements such as availability, emergency scalability or backups yet)