The SC/Rambler is known as a giant killer due to its low weight, and in base form outran virtually all of the big 3s base muscle cars. It took 396/375, COPO, Cobra Jet, 440/6, Hemis, etc to beat the lowly little AMC. AMC guys could add the Group 19 performance parts and get into the mid 12s, but it wouldn't be fair to compare a modified 390 against a factory built car with their optional high performance engines.
And considering AMC only built about 300,000 cars in total in 1969, 1,500 total SC/Ramblers isn't too bad.
Edited to add, I agree with GasGuzzler that that calling the Mach E a Mustang is a lame move by Ford......