Earlier quoted context omitted.
I am biased but I can tell you what works best for mid-large companies: having a solution provider. Basically a partner that hosts and maintains the instance and has enough Atlassian certified people to help you with any question so that you will never have to hire people to just maintain the beasts or tell you about features, tricks or plugins that could solve problem X. Experienced people hosting and tuning Atlassi…
I can't see the difference between a "solution provider" that hosts your Jira and just getting Atlassian to do it. What's stopping the solution provider from accidentally running a script that deletes some customer's files and struggling to do a partial backup restore?
Many medium-large corporations have their own cloud environments that their IT Ops control. Solution providers can host Atlassian stacks on their own cloud environment where they are not affected by data privacy concerns (it's in their already green-lit cloud providers data center) so they can host it behind a firewall with only VPN access allowed. They can also do all the magic you can usually do with web software like put a frontend proxy in front of it, or use more flexible/legacy authentication methods. Not to mention that for example you could have a Jira Cloud that you would need to integrate with a SCM program. Jira data could be "OK" to live in the cloud but code would be a big no-no. These problems can be solved by having them all live behind the firewall.
A competent managed solution provider also has consultants that can train or instruct on usage. It costs but it is simpler and faster than having to go through the forums or send a support ticket for every small issue to Atlassian itself.