Yes, for the love of gawd, stop thinking everyone is related.
Also, Urizen is wrapped up in vines that look a lot like the Qliphoth's, perhaps Vergil's body is legit being used as a vessel and the roots are like...the Qliphoth controlling the body. I dunno, certainly makes V's remarks not entirely incorrect.
In my opinion I think people would want V to be related to the sparda line because of the dynamic it would create with having Dante and Vergil's two sons fighting alongside eachother and carrying on the legacy of Sparda after Dante and Vergil are gone since this game has been teased to be the final chapter in the sons of Sparda storyline. Also having V related to them would better explain how he would be able to contend with the top tier demons he will surely be fighting in this game.
As was said earlier him being Dante and Lady's son would be possible and would explain his black hair since Lady has black hair.
It's a shortcut to get people invested in him.
Nero would have benefitted more from being introduced as the motorcycle at the end of DMC2. Making him Dante's kid who comes to ask his dad's help for something pressing. He finds lucia and bam you have avoided half of Nero's actual problems and given audience more of a reason to care.
Granted his dynamic with Kyrie is gonna need a lot more work.
Granted the main problem with V being Dante and Lady's kid is where the heck was he during the anime/4? Hell the anime would have actually had stakes if Dante's actual kid was involved.
I'm ok with him not being Dante's kid but I rater just play as Vergil tho. V could've been DLC.