By defense breaking you mean a final through ball past the defensive line, correct?
Frankly, that doesn't really matter much at all. He doesn't need to be quite at that Xavi level, making through balls that go past 5 or 6 guys to create a chance in the final third. We have Coutinho, Messi, and Dembele to make all the key passes in the final third we'd ever need. Plus Griezmann who makes associative play around the box possible on a regular basis unlike Suarez who totally ruins these plays.
What we need from Arthur is great ball retention (check) and, more significantly, the ability to break the lines in MIDFIELD with splitting passes. That is something Rakitic horribly fails at, especially in a 4-3-3, and why we struggle to get the ball to Messi in the CL unless he practically drops down to pick it up from Busquets.
Modric doesn't really make that many defense breaking throughballs. He creates quite a few key chances tho and has a lot of "pass before the pass" plays. Kroos on the other hand really doesn't do either of those things that regularly, most of his assists come from set pieces or a random cross here and there. And RARELY does he ever get assists in the UCL, let alone significant ones in KO stages. The thing is, that those crosses/set piece assists aren't what make him world class and he would be world class without them. Just as Arthur can be for us as long as he's able to keep the tempo and keep the ball progressing in the midfield.