C++ succeeded because it was Object Oriented, people didn't start talking about RAII as C++ killer feature until years later
python succeeded because it wasn't Perl's TMTOWTDI, everyone expected ruby to overtake python, but .. for some reason that never happened
swift succeeded because apple pushed it to replace objective c, that if you consider swift succeeded
anyway, i agree with your premise, languages need one key strategic advantage feature to succeed, but you just got it wrong on few of them .. and if i am wrong too, then the premise is weak, if we are not sure what the killer feature is, we then have no idea why the language succeeded
python succeeded because it wasn't Perl's TMTOWTDI, everyone expected ruby to overtake python, but .. for some reason that never happened
swift succeeded because apple pushed it to replace objective c, that if you consider swift succeeded
anyway, i agree with your premise, languages need one key strategic advantage feature to succeed, but you just got it wrong on few of them .. and if i am wrong too, then the premise is weak, if we are not sure what the killer feature is, we then have no idea why the language succeeded