For example, of course only QA people can use "Testing passed" transition. Of course there should be x, y, z fields filled out to be able to create the ticket. Well we're at it, let's make sure only the product manager can close a ticket with 'wontfix', and only the release manager can change a fixversion.

This is a really common problem with any workflow tool, where well-intentioned control points get in the way of actually Getting Things Done, both from the perspective of not thinking through all the complex scenarios (what? I have to fill out 5 fields before I can close this as a duplicate??) and from not trusting your employees (don't worry, a jr. dev is not going to re-assign a fix version even though they can -- or at least, they won't do it twice).

I've had some fairly large teams able to use JIRA without a single workflow customization (especially with Agile). We've added custom fields and such along the way for better reporting and such but there is definitely some mileage you can get out of the box with it.