By several soldiers, you mean....two, right? The anime greatly exaggerates Mikasa's OPness. And battles aren't determined by the actions of the individuals. All things considered, Levi and Mikasa can't teleport, not to mention that there were only...what, two, three large-scale battles in the anime? The flashback thing where everyone was a kid, the Trost thing where the scouting legion weren't even there (thus no OP Levi), and...that's the only two large-scale ones in the anime. In one case, the Scouting Legion had just returned after getting their ass kicked. In the second one, the Scouting Legion weren't even there.
Heck, just because the Scouting Legion is filled with humanity's strongest doesn't mean that they're obligated to win any battles. Considering how there's one way to kill titans and a few dozen ways to kill humans, it's not surprising that they've just been constantly losing.
The ending was filled with hope, and they actually did learn a lot. Crystallization of titans (dat foreshadowing with that glob of crystallized titan barf in the early eps), the ability for many to transform into titans (with the high possibility that most of them are antagonistic), and...the titans in the Walls. Hue.
But yeah, I'll concede that the anime dragged everything out a bit too much. It's a monthly manga, so they don't have many 'good' points to end off, all things considered. There is a lot of stuff they figure out and foreshadow and imply in the manga though. 2nd season would be nice if they get to the whole experimentation part.
And I guess it's just your taste in the end that's preventing you from enjoying the despair. Bet you wouldn't like Knight Run then...bah.
