Haven't seen him being a good controller though. Xavi looked so natural in that deeper role ever since he made the debut.
But yeah, it's tough with these comparisons.
One doesn't necessarily need to begin as a 'Xavi' to end up becoming a controller. Thiago was more attack minded in his early days but added patience and tempo to his game over the years. Kroos had an even more radical transition from an attacking mid to deep lying controller.
The real indicators as to what role Aleña will eventually take are his skillset. He turns into space, routinely plays off teammates in 1-2's, passes between lines, and generally navigates the pitch looking to get involved wherever. He's really similar to young Thiago in that regard. Not the most imposing presence in any one area of the pitch yet, but involved and active in all phases of buildup play.
Once he starts playing more minutes with the first team he'll settle into a bigger role with bigger on ball responsibilities. As a youngster his focus is really about constantly moving and providing support rather than being the primary initiator or running the play. Patience with the ball and confidence to be a primary outlet are both things that come in spades with age and experience; even if he doesn't become as ball dominant as Xavi he still will probably be a creative and tempo setting player in the midfield.
And if Arthur+Aleña really is the future of our midfield then both of them can combine into a well controlled and rhythmic duo. Neither has to be the distinct 'Xavi' or 'Iniesta' but they can form an imposing unit with Busi to control the midfield and set up an offensive transition.