Zidane is not overrated at all. Of all the players you have mentioned only Ronaldinho is on par with Zidane. It’s not really about how consistent they were as Ronaldinho is not a consistent player as the likes of Scholes as already mentioned, but rather it is the memories of beautiful playwork, dazzling dribbles, outrageous skills, and bewildering passes that set up goals for other players that a player such as these two have done on numerous special occasions which then sets them apart from other very good world class players.
I would include real Ronaldo in the same bracket as Zidane as well, whereas the other players you mentioned were very good world class players albeit not in the bracket associated with supreme greatness for this recent generation. Every generation I believe has just a few, currently, I think in time Messi will be associated among these elite group of players.
Really I think it's all about the degree of memories they leave on the mass footballing public.