Well, maybe if KC opened its doors to the international stage and probably changed some gameplay stuff they might be able to compete with AL a bit better.
In terms of art, I really like KC overall compared to AL since the former does almost signifies what the ships were back in the day. The best example I could probably give about this is IJN Nagato. In KC, Nagato is a powerful, stern-looking ship girl with an intimidating and commanding aura around her. In AL, Nagato is a loli that just doesn't have that same aura around her as she's more of a shrine maiden overall. While I have nothing against lolis and shrine maidens in general (ESPECIALLY SHRINE MAIDENS), I just don't really like what AL did to one of my favorite ships in history.
In terms of gameplay, I really like how AL has a skill system for each ship class just as Girls Frontline is with their T-Dolls. Although unlike the latter where every T-Doll has there own skills, the former at least has a general skill depending on the class of warship. To add, AL has a system wherein you can visibly see which position a ship girl is whenever they are engaged in battle with their character sprites. Plus that thug life Prinz Eugen after every engagement is hilarious!
But that's just my opinion on both games. There are some things that I see between that are both good and bad. At the end of the day, however, it still pretty much boils down to personal preferences. If you ask me, I would still play KanColle more not because I've been playing it for a really long time, but because of the history of each ship girl that coincides (almost) with their personalities. Also, Intrepid is the only potato that I really like that Shibafu has made. She looks quite... motherly.