To me, they are just very different courses, and different skill sets, so can't really be put in a "hierarchy". It depends what you want to do, and what skills you are looking for.
The Powerboat Instructor course is all about teaching Powerboating, focussing on the Level 2 course. How to structure sessions, how to teach, giving feedback, coaching people, etc. You need to be able to demonstrate Level 2 standard boat handling skills as part of that, but the course is focussed on how to teach and coach people and how to successfully deliver an RYA Level 2 course as a new instructor, not really about improving your own personal power boating skills. The only formal pre-requisites are that you have completed the Level 2 course yourself, have a valid First Aid certificate, and pass the Pre Skills assessment. Whilst it can obviously help you in your teaching and background knowledge, you don't need to have any more advanced boating/power boating skills than Level 2.
Intermediate and Advanced are both courses designed to improve and grow your own personal power boating skills.
The Intermediate course looks at planning and executing short cruises by day on a planing powerboat:
https://www.rya.org.uk/courses-train...ermediate.aspx
A big part of the Advanced course is about how to safely plan and execute a night passage on a planing powerboat:
https://www.rya.org.uk/courses-train.../advanced.aspx
The Advanced CoC is a commercial RYA/MCA exam (not a training course, although often coupled by schools with training, or taken immediately after the RYA Advanced 2 day course), designed to validate that you have the required skills to skipper powerboats in a commercial working environment, including coastal trips by night:
https://www.rya.org.uk/courses-train...-advanced.aspx . Very much a test of your own powerboating and navigation ability!
Yachtmaster (Power I assume, not Sail) is from the "big boat" scheme, and more designed towards larger more complicated motor cruisers, longer multi-day trips, more navigation, etc. Some crossover with the Powerboat scheme in terms of core skills, but really aiming at a slightly different use case than RIB's. The Yachtmaster Power CoC is similar to the Advanced CoC in many respects, but taken aboard a larger motor cruiser.
Regards,
Paul