This may not matter much, but strength and stiffness are not necessarily proportional. Epoxy stiffness (not necessarily industrial strength epoxy):
https://netcomposites.com/guide-tools/guide/resin-systems/strength-stiffness/
Stiffness of epoxy from chart is 3.5gpa which is ~508ksi, compared To 10700ksi for aluminum or ~30000ksi for steel.
Therefore, regardless of strength, a layer of epoxy will be 21 times more flexible than an equivalent layer of aluminum and 59 times more flexible than steel. Given a thin enough layer of epoxy, this may not have a significant impact on rail mounting. But, a 500lbf bolt preload over a 1in^2 of .25" thick epoxy will cause ~.0002" of deflection in the epoxy layer.