I don't think anyone is directly stating centers aren't relevant, but they are alluding to the position as being less important.
The difference right now, is that very few centers are beasts that just destroy people in the paint. Embiid does. KAT does to a much lesser extent. That's what Ayton needs to become. As others have pointed out, the center who shoots the three should never be as valuable as the center that can shoot 60%+ near the rim.
If Ayton improves marginally as a rebounder, but can become a force at the rim, the Suns will contend for a long time because few other players have that skill in the modern NBA.
I'd take Ayton over Jokic if that's what he becomes.