>>>Thrust reversers are only considered an aid to landing operations, and when an aircraft's landing performance is calculated, it is assumed that the thrust reversers will not be used...just an aid...
I think the, "it's just an aid" argument is taken out of context.
The thrust reversers are omitted from rejected take-off calculations not because of the minimal impact they have in shortening stopping distance, but rather the opposite.
They are basing a rejected T/O on an "almost" worst case scenario. No T/R's, brakes worn to minimum (less able to absorb kinectic energy), etc.
This is because they want to base stopping distance on the bare bones equipment to stop the airplane. You can bet that if T/R's were thrown into the equation, stopping distance would be further reduced. The exact amount or percent I don't know.
I might point out that regulations require airplanes reach V2
speed no more than 35' above the runway with one engine out. T/O calculations are based on having lost an engine at V1.
This doesn't mean the extra engine is merely an aid after V1.
It's basing the numbers on conservative worst case situations, not optomistic projections.
You're only as good as your last departure.