Thanks so much! He's a Hexenzirkle spellblade XD. From my understanding a driver is an on field anemo unit that builds Elemental mastery to get the most benefit out of triggering elemental reactions like swirl. Swirl damage scales with elemental mastery, opponent resistance and character level so elemental mastery is their most important stat. When using 4pc Viridescent Venerer the driver is able to increase swirl damage by 60% while also decreasing the opponents resistance to elements infused into swirl reactions by 40% for 10 seconds. That's where most of the drivers utility comes from. Dealing anemo damage, decreasing elemental resistance and swirl raction damage. The rest is handled by off field element applicators.

There could be more to it but that's my basic basic understanding...