Well, you can't use Tyranitar in Reborn online due to it not being legally obtainable in Pokemon Reborn as of Episode 16.
Also, you cannot really compare Excadrill to Tyranitar directly because they are two different types of Pokemon that play different roles.
If I had to formulate an argument on this, I'd say Tyranitar is used more often due to Dark Type moves being so good and the fact that it sets up Sandstorm.