Did you clear out the Rocket Hideout in Celadon Game Corner? Your team is quite under leveled. Koga's lowest level Pokemon is Level 37, and that's two levels above your Venusaur, who is the highest leveled by a lot. You should grind your lower leveled Pokemon, Arcanine would be incredible if it was the same level as your Venusaur. Mud Slap on your Dugtrio is not useful. The fact that you have two Pokemon that you probably can't evolve being Kadabra and Graveler isn't good for your team. They will quickly become obsolete for you, especially Kadabra, as you will find it not being able to survive a single hit.
Considering you have both Graveler and Dugtrio, I don't think you need to grind a new Diglett to get Earthquake now, since you'll have it before the E4 when it learns it at Level 51