flybymike
The MEP revalidation is a proficicency check, and is a test in the sense that you pass or fail it, though examiners have quite some flexibility in asking you to redo unsatisfactory parts of it on the spot. The route sector part is, as you deduce, a bit of a red herring. You certainly have to sign a CAA form at the end of it.
The good news is that a successful MEP skills check (or another test like an IMC rating or IR renewal) can substitute for the training flight required to revalidate the SEP by experience. There should be no debate about this. Note that you're still required to have the 12 hours in SEPs in the 12 months preceding expiry of the rating -- the MEP proficiency check does not substitute for an SEP proficiency check, only the training flight element if you choose to revalidate by experience.
The debate about whether the training flight can, in effect, be failed by the instructor witholding his or her signature will run and run. The flight need not follow any particular pattern, but you can't force an instructor to fly do a flight with you that they don't want to do, so if they insist on a flight that doesn't follow the AIC recommendation, find a different instructor.
Sliding member
If you don't revalidate by experience before your rating expires, you must take a proficiency check with an examiner to renew. You can do this after the SEP rating expires and the proficiency check for renewal is no different from the check for revalidation.