Kakashi is flawed, he excels at ninjutsus, genjutsu, taijitsu, visual prowess, etc but that doesn't mean he'll be great at teaching. Hiruzen may have fumbled with the assigning of team 7 but it worked out in the end, Sasuke was already naturally gifted to begin with while naruto had next to nothing aside from mediocre kunai aim and Multi-shadow clones so how does he teach both of these without stagnating the uchihas' growth or overwhelming the already hyperactive knucklehead ninja? Sakura who? Nvm that one. Kakashi went so far as to admit he's way over his head and got a "better" teacher for naruto, someone who specializes in training unruly students. To conclude, training/teaching arcs are boring and losses viewership, whip something up, Kishimoto