I've seen heard this opinion a number of times and I don't believe it's true. TargetProcess is a better project tracking tool. It has a deeper hierarchy for organizing work. It has the concept of teams built-in and allows you to view work across multiple teams and/or projects. It also provides a way to do roadmaps built-in. Everything is included and everything is designed to work well together.
As for the specific criticism about not being able to get a high-level and low-level view in one tool, I think the reason why JIRA does poorly at the high-level view is that it has a very shallow hierarchy of work entities. It has epics => user stories => sub tasks. While projects can also be used to organize work, JIRA unfortunately binds the concept of sprints which is more of a team thing to projects. Thus it's difficult for one team to work on multiple projects or multiple teams to work on a single project.
TargetProcess on the other hand has a separate entities for teams and sprints which allows projects to be used for organizing work. It also has an additional level in the work hierarchy providing the following levels: project => epic => feature => user story => task. This deep hierarchy allows you to group work into larger groups allowing you to see both the high-level and the low-level.