PA28 Checkout
What is the purpose of the checkout?
You are a qualified pilot. The checkout is not a training flight! The purpose is to give you the opportunity to discover before flying PIC the full operating characteristics of the aircraft and to know it's best operation - in accordance with the Pilots Operating Manual. For you to have the fullest knowledge this should be practiced throughout the whole of the a/c permitted operating envelope.
The time it takes is the time it takes. It is quite proper for the school to insist that the flight is lawful. But if the aircraft is within the c of g for the exercise i would have no problem having another qualified pilot in the back. I would not want a non flyer when we intended to do relatively high G manouervers such as in steep turns and possibly negative G with stall recoveries.
I find that it is very rare for a current pilot on such as a PA28 to do more than a single upper air review plus a circuit detail to complete. If done in one flight 1:30hr would normally be max.
Who is saying all that you have reported? Does the CFI know what is being said to you. If it is the fancy of a single FI without justification then the school shouldn't suffer. The CFI should be made aware and may resolve the issue.
If it is the policy of the school then as others have said you have a pair of feet.