I don't believe Carrot's shown what she can really do, and we may very well see that moment very shortly. You can come back and quote me on this.
I provided the official translation. They didn't see "shadows" like the fan translated scans, they saw people. I.e. Usopp spotting the guards was nothing special since others, without binoculars saw them too. It wasn't being highlighted, unlike the fact that he put them to sleep was.
Carrot spots something and then shouts down to the rest of the crew alerting them of the danger. Usopp spotted some guards (that others also spotted) and then sniped them, because he's the sniper.
Carrot's significance in the lookout position lies in the fact that she consistently did it a vast number of times. Not in any of the actual feats in WCI alone, since none of those were individually impressive.
I'm not saying, "Carrot's already amazing lookout, she can look through binoculars". I'm saying, that when working on the ship, Carrot has consistently found her role in the lookout/scout position. Even in her very introduction into the series. It is therefore possible that Oda will reveal her to have a talent at doing so, just like he did with Jinbe who had helmed before in the series, but all of a sudden had a huge focus put on his ability to do so that didn't previously exist.
1. Usopp does have the attack power to deal with that arm
2. Franky was the only one to actually shoot at the Kraken. Chopper just blocked and Robin pushed the ship away from danger. Franky literally fired projectiles at it when they were in a situation where they needed to attack it from a distance. A situation where the sniper should be the man to call.
3. Usopp then does almost the exact same thing as Franky a few chapters later and is also praised.
Actually Franky is able to play music to influence Luffy's mood.
This took place in the very arc that they got an official musician, despite it already being shown that Luffy loved Franky's music. At the time you could bet that people would point to this as proof that a musician isn't needed since they've already got Franky who has on multiple occasion whipped out his guitar to Luffy's pleasure.
That aside, I understand each straw hat can do something in their role that none of the others can do, hence why I expect Carrot to do the same shortly.
Jinbe had already helmed on a ship when they were rushing as fast as they could to Marineford to go save Ace. Jinbe was helming and there was zero focus on it. That would've been the perfect opportunity to reveal, "Wow, you're an amazing helmsman Jinbe! We got to Marineford so fast all because of your incredible skills at the wheel!" That never happened though. And zero attention would be drawn to his skills until another 300 chapters after that, until a situation was specifically created in which Oda finally wished to reveal it.
Yeah, I agree there were opportunities for Carrot's skills to have played a role. But I'm also aware that Oda's not always consistent in doing this and these skills come second to the plot. There are instances in which characters have a skill that could easily solve a situation, but they simply don't. Law choosing to leave Momo to his fate a few chapters ago for example. Or any of the others not doing anything about it.
That doesn't mean he will never showcase her ability though, and as I've said, I believe he will do so very shortly.
Jinbe had a whopping 300 chapters before his reveal. I think Carrot's fine.