It is hard to detect subtle manipulation period. But assembly language is an extremely concrete representation of a program; it is not an especially great way to write underhanded code.

It's possible to write obfuscated assembly, of course, but it sticks out as obfuscated.

To further get your head around the lack of cover compiled code would give a backdoor, it's worth knowing that Hopper will give you serviceable C-ish code from x86_64 for... let me check here... fifty nine bucks.

(It's possible that my only message with that last graf is "Hopper is great").