The reunited group argued that a lot of Simon Cowell's latest boyband's fame worldwide has stemmed from Twitter and Facebook.
"We didn't have social media back in the day, we didn't have Twitter, Facebook, web chats, nothing - we just turned up to places," Scott Robinson told Heat.
"Whereas now you can be in the room straight away with just one tweet."
Sean Conlon added: "Would One Direction be as big in America without Twitter? That's the question." Robinson replied: "No. They. Wouldn't."
Conlon added: "I'm not sure either. We had to be there, didn't we? If we weren't there, we weren't there."
ITV2's The Big Reunion - which has followed the reformation of 5ive, Atomic Kitten, B*Witched, Liberty X, 911 and Honeyz - concludes on Thursday (March 28) at 9pm.
Watch a megamix of 5ive's greatest hits below: