It's not that stock triggers are bad, per se, it's that for a competition handgun one can definitely improve both splits and accuracy by improving the trigger. Don't care who you are, dropping and smoothing the trigger pull, shortening the reset and creep all help with both.
Rob Latham, Max Michel, Ben Stoeger, and a bunch more pros all run the best trigger pulls whatever division they're shooting in allows. I've taken classes with both Latham and Stoeger, and they both advocate running the best aftermarket or 'smithed trigger you can.
My glocks are pretty much competition only, with a bit of plinking thrown in, so I want the fewest impediments to stack on top of my already abysmal abilities. I've never won a match, but I've also never come in last- so far
I prefer the factory Glock 17 trigger because it isn't grooved. I have put G17 triggers in my G19's just because they are smooth face. I polish up all contact points and put in a Ghost connector and call it a day.