Processing Rules are pretty powerful (at least have ability to destroy our data) and therefore there was a point in time when those were only allowed for admins with a specific certification.
But since then the UI didn't improve much (I think that just the original limit of 50 rule sets per Reporting Suite was increased and extra condition with a rule action was added).
But we still have major issues with using Processing Rules - namely:
Is there any hope for improvement?
Yes, there is a lot of work needed to make the processing rules UI more user-friendly. I share many of the same points of feedback you've listed above.
I also would love to be able to delete context data variables from the list once I know they are no longer being sent in current requests.
Also, when editing a rule, I hate that you can only insert new actions at the bottom and cannot drag and drop them to where you'd like within the current rule.
Many, many more.
I had a meeting with some Adobe product folks today, and I am cautiously optimistic that they are paying some attention to feedback about processing rules right now. Don't give up hope yet!
A lot of the issues you mention (e.g. slowness) are likely due to outdated API built around the processing rules CRUD. It may be worth supporting the requests for updating the API on the ticket, here, which would also enable easy fixes in the UI.