You can workaround this issue by creating a new issue type and adding it at whatever level you want in the hierarchy

I'm just starting on using Advanced Roadmaps, and already it is clear that one global hierarchy per instance is going to be problematic for us. 

The way to make this work for large enterprises is to enable multiple hierarchy templates/schemas that can be applied to many projects

be so that hierarchies work as schemas in Jira and as Admin you can design a number of them that can be used by the projects in your Jira instance. (or Jira cloud)

I worked with 75 ARTs whereof 12 or so ARTs built up 3 Solution trains. So all 75 ARTs had to ignore the capability level in all create screens and other configurations like the parent field. It would be great to have the flexibility to connect one hierarchy template/schema to a group of Jira projects.

It's a real limitation that plans require a single global hierarchy. In order to link work across projects and build communicative roadmaps, we often want to group and roll up issues differently. 

We need this improvement as well. Organizations have different teams with different needs and they require different hierarchies.

I guess Steve a 4000 user license is not much motivation. Makes me want to take my vote back for our tiny little site.

This is incredibly important. I am working with a enterprise that has multiple 10000+ user instances. Having hierarchy defined at the global level is making this an extremely hard sell – The teams were highly interested until they realized that they will not be able to define hierarchy, but rather the IT owners of the JIRA application will have to configure the hierarchy for all teams.

Effectively this is a non-starter: My customer is approximately 4000 users, however they are in a JIRA instance with 10000+ users. They will not have control of the hierarchy relevant to their organization so we are required to pursue other options.