Krillin is Hurr durr.
The big problem with Krillin killing everyone is the villains that come after each Saga.
If Krillin kills Nappa, no time to stall Vegeta. Vegeta wastes everyone before Goku arrives after seeing how threatening they've become.
Krillin kills Nappa AND (by some miracle or teamwork) Vegeta, there's no reason to go to Namek (assuming Piccolo would live). Freeza Gets the dragonballs GAME OVER. (he may not get his wish though, since he needs to know the password)
Krillin kills Freeza, Goku can't go super saiyan, everyone gets wasted by the Androids.
Krillin kills Androids, Everyone gets wasted by Cell.
Then after 10 years… Buu would inevitably come, and Everyone dies unless Goku gets a spirit bomb, but he wouldn't have met Mr. Satan.
Krillin NEEDED to suck.
Toriyama could've gave him some more victories sure, but he had to be stupid so everyone else could get power boosts.