How the fuck was it obvious? Please explain how a reasonable person would think Nero is Vergil's son based on the events of DMC4?

" And from that day, my arm changed, and a voice echoed, power, give me more power! "

If anything, DMC4 implies that Nero's demon arm IS Vergil. That Nero's arm is possessed by Vergil. Nero was attacked by something, his arm changed, and that's why Yamato reacts to it, and that's why Nero's devil trigger has Nelo Angelo in it.

There is not a single fucking event or piece of dialogue that points to Nero being Vergil's son, let alone it being OBVIOUS. That's not even mentioning the timeline issues of Dante and Vergil being 19 in DMC3 yet in DMC4 Vergil had been old enough for Nero to be in his 20's..

I will not sit here and allow you or anyone else to insult me and tell me it was fucking OBVIOUS that Nero was Vergil's son. The narrative, like much of DMC4, was unfinished.

And finally, I don't think the team confirmed it for YEARS after DMC4.