If that really is what you do on a simple SEP Class Rating revalidation proficiency check , then the moral of the story for any pilot in your area must be FFS revalidate by experience!
Why wouldn't you expect proper flight planning for a prof check?
Both of the schools I examine at have simple and easy to use mass and balance sheets and performance graphs readily availble, It shouldn't take more than 3-5 minutes to come up with some sensible figures, if pilots are too lazy to complete this simple task then I would certainly question them to assess their level of knowledge and understanding.
Not saying I would fail them, but I'm not about to sign someone off having no demonstration that they understand the performance limitations of the aircraft they fly.
This is factored against both schools being based at airfields with very long runways. It is an unfortunate result of this that pilots become complacent and forget the exact performance capabilities of the aircraft, and then incidents result going to shorter strips.
This is the one opportunity in two years to bring these pilots back up to standard, why would I skip it?