People seem to be confused about the series of events when it came to DmC's little "family murder" thing.
! Sparda helped Mundus gain all his power and become a demon king. So hint, hint Sparda was pretty damn good at his job to have been the one that Mundus counted on the most.
@ Sparda fell in love with Eva and up and left, ****ing Mundus off. They hid out for a while and had some anklebiters
# Mundus found Paradise at some point, and Eva distracted Mundus' forces while Sparda took the kids and escaped. Unfortunately, Dante followed Eva, and saw Mundus rip her heart out before Sparda found the kid and took him away (this is also how Mundus was privy to a son named Dante).
$ Sparda armed his kids with Rebellion and Yamato, locked their memories away, and hid them in orphanages where later on Vergil was lucky enough to be adopted by a nice rich family, and Dante was...well...we see what happened there.
% Sparda confronted Mundus to distract them from looking for Dante, and was either defeated by an immortal jerkoff using a Hellgate, or willingly sacrificed himself. In all reality, he was probably imprisoned and tortured for Dante's location, which he never relinquished, leading to his banishment that we know he suffered from.
Sparda didn't lose to Mundus during the attack on Paradise, that was Eva. Sparda also certainly wasn't some weakling either, he was one of the most important people who helped Mundus attain power of the demons in the first place. so he didn't previously defeat Mundus, big friggin' whoop.