These are some intriguing observations you've made and certainly begs the question of a proper payoff for Carrot. There are too many strong suggestions from Pedro's line to Carrot to the latter carrying the former's that we will see Carrot again. When that may be is anyone's guess at this point...
Oh, you mean how like Yamato was a lock for the crew from the start until she declined? Why don't we see how Oda chooses to progress his story before we pass on judgment as to whether Carrot will join or not?
You're not alone friend. I had that same feeling too. And besides, Momonusuke sure could use new retainers to honor the positions previously held by Ashura Doji and Izou (RIP to both) or better yet, be his bride to become the most powerful couple in OP.
Awww man, I've been vouching for Carrot for a while, but I became content with Yamato joining the crew. Even still, I pretty much knew it would turn out this way given how Oda made Jinbe say "the captain decides that."