Couple lore questions

I just finished DMC Season 2. I've played DMC5 but I'm definitely not a huge lore expert. I'm also not sure how lore accurate the show is, so I have a few questions after watching it.

• How was Sparda powerful enough to match defeat Mundus?

• Why are Mundus and Argosax gigantic now when the flashbacks showed them as normal sized demons?

• Does Vergil really think he can solo Mundus? He and Dante couldn't defeat Argosax together, and Mundus is supposed to be even stronger. So why does Vergil suddenly think he can kill the guy who beat an enemy that he and Dante struggled against?

• Why doesn't Vergil just work with Dante to kill Mundus first and then turn on Dante afterward if that's what he wants?

• Does Vergil actually want to kill Dante and take over Earth? If so, why not kill Dante first and then fight Mundus, or team up with Dante to defeat Mundus and deal with Dante later?