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:
the UI is cluttered and slow
there is no way to properly debug (only having a staging suite to test those and a production one to copy the tested rules to, autocomplete in combo-boxes also helps a bit, but that is still insufficient)
contextData that is not mapped is lost with no reporting around this
ordering doesn't make much sense - rather some form of relations in between particular rules might make sense
when tracking many different properties into one Reporting Suite, some sort of grouping would be helpful
relation to Mobile Services is a bit weird
some search/filter feature would also help (now we use opening of all rule sets and then CTRL+F)
A lot of the issues you mention (e.g. slowness) are likely due to outdated API built around the processing rules CRUD.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.