I like Sakura because she is cute, stubborn, devoted her feelings to one person and kept at it for a long time, in Shippouden her resolve not to be a burden changed her, in a normal fight she now stands a chance, but in a league fight she will lose, lets face it, Sakura is on a average level, while Naruto and Sasuke are like Vegeta and Goku compared with Kirririn (or what it was the guy without a nose), sure he was strong, but dude, can you see that aura ?
It's a whole different level, Ino and Sakura are even in their league, just like Ino and Sakura both would lose with Naruto or Sasuke, you can't have only all powerful people around you, you need to balance the reality and show insane superiority, by having a weaker member in the team, Ino Shikamaru and Chouji, which of them would win ? Shikamaru likely, but if by some twist of fate Ino would overpower them, that would be great.
In Fairy Tail, Lucy isn't a powerful wizard, more likely she is just your average boing blonde with some celestial keys to summon spirits, but we did see what she will eventually be able to do later on, that spell he put in her was amazing. No one is useless in a show, unless they were made that way, but Lucy and Sakura did prove to be reliable, it's just that it seems they are useless considering the level of enemies they are about to face on a regular basis.
