I really do understand the difference between the two.
Basically one is a very strong sheet material that is almost impossable to puncture or tear... that doesn't have any plasticisors to off gas,that can be formed with heat if required... it can also be welded. TPO... lifetime is very long
The other has placticisors (Pthalates) that off gas and get brittle over time... that you mop, ot brush, or squeege and looks like thick paint, and well yes acts like thick paint. EDPM... the hotter the sun the shorter the life.
I can explain the process with chemical formula if you wish... most of my life I worked in a large national lab... and actually remember the time before plastics.
When you think rubber... think cracks in the sidewalls of tires as they age.
I will agree that EDPM is cheaper.