1.It states Sakura grows up to be the best in Konoha not the world
2. Since it states "she grows up to be the best in Konoha" Its pretty obvious that she wasn't the best in Konoha (Let alone the world) at 17.
3.Tsunade was noted to be inherently strong (Sakura was not) on top of being able to utilize her chakra to increase her psyhical strength Sakura's only true feats were during the war which she displayed a great display of psychical strength that Tsunade showed during her fight with Orochimaru HOWEVER Tsunade was A.Tsunade was using chakra at all times to conceal her true appearance and B.Using chakra she had at the time.Sakura was A. In the prime of her life. B. Storing chakra for the bette part of two years before the war began.
Sakura could never display the strength she showed in the war on the fly and her abilties while powerful her actual feats and potential are greatly exaggerated
Not really surprised with people that've "read" the Naruto series and haven't figured out that Konoha is pretty much the center of everything. Thus:
Strongest shinobi in Konoha = strongest Shinobi in the world
Second strongest in Konoha = second strongest shinobi in the world
Best scientific research in Konoha = best scientific research in the world
Strongest medical shinobi in Konoha = strongest medical shinobi in the world
Strongest genin housewife in Konoha = strongest genin housewife in the world