As previously, show me a 50 year old EPDM roof? You can't, and do you know why, they've all failed. The early ones lasted 5 years if you were lucky. I spent 3 years at Brent Cross Shopping Centre stripping up 16000 M2 of it after it failed prematurely.
Installed exactly as specified, but due to inability to suffer thermal movement over a long period it rippled and separated on the seams.
The details also failed early due to different temperature absorbtion to the flat areas, and shading of upstands again leading to thermal stress causing de bonding.
On top of that, we have also stripped up over a 100 schools over the last 30 years covered not only in EPDM, but also GRP systems.
You contradict yourself saying;
In addition, installation details have been improved to ensure even the largest of roofs can be accomodated without problems caused by expansion/contraction.
You've just identified there have been known issues. EPDM as a material may well have a 50 year lifespan, the products that bond it do not.
And after 50 years, it will not be in the same shape form as when it was laid.
A single sheet on a back addition may well last a while, but it is usually installed by builders, not roofers.
While understanding that people have to earn a tanner the best way they can, touting something as something it is not is wrong.
As Noseall has said, a pitch conversion is not that expensive and will always look better than a flat roof.
Everest have undoubtedly attempted to rip the OP off, thats why he's here. Not for a sales pitch.