Just because a fin is carbon does not nessasarrily make it better or faster than a very well designed G10 fin. IMHO, carbon is not usually much of an advantage in slalom fins under a certain size, around 30 'ish cm depending on design. But I admit I have not tried a great many larger carbon slalom fins.
Highly raked weed fins must be as stiff as physically possible, which is optimised by carbon. But weed fins are also subject to a lot of abrasion in many tyes of weed, so that skews the advantage back to G10.
And then there is the fact that certain boards just like certain fins. Those that were your favourites in one board, may not have the same magic in a another similar, but different, board.
As always, it's horses for courses, and in the end, you can buy the most highly recommended fins to reduce the chances of it not being ideal, but that is still no guarantee. It still often boils down to 'suck it and see' to find that one 'magic' fin.