Is Varka strong solo or are the test runs rigged?

I got back into Genshin after Varka's banner ended, and playing him in Nicole's test run is insanely powerful as a team. But then I played him alone in the test run, without using any other abilities, and he was still very strong. If you look at his character details, he doesn't have that crazy of a build.

So I guess my questions are:

Is he really that good solo (with anemo and pyro team for resonance/reactions)?

Are Durin and Nicole providing some crazy dmg buffs passively?

Or could the dmg in test runs be tweaked to make the characters seem more appealing?

Sorry if this sounds dumb. I haven't played in a long time, and hexenzirkel & lunar reaction teams are soooooo much to comprehend, and I don't understand them much. Appreciate any answers!

Additionally, could I get Varka to have a similar damage output if I'm not going to pull both Nicole & Durin?