That one player..

Yes, he's either brilliant or awful, rarely is he in between. Maybe, but he still has 50+ international goals.

Does this not apply to Messi to a certain degree? that is not so bad in my opinion. Every single player may have a bad day where nothing works, even great players like them. But as I said before in terms of Ronaldo both are dependent on the team. Look at the squads in which they play. If the players aound them are good, so they are good as well. But if they are bad, the same applies to both Ronaldo and Messi. In my opinion a great player is the one who is able to carry his teammates along in bad matches.

I don't think I've ever seen Messi have an awful game, there's been games where he has little influence, but never actually detrimental to the team. Ronaldo can let Madrid down when he's bad.

I have seen an awful one by Messi indeed. It was in 2010 at the World Championship in South Africa in quarter finals where Argentina was humiliated by Germany and lost 0-4. Messi has not played a good match. Anyway he has not played a good tournament in that year for Argentina.

You are comparing different positions so its not easy.

Zidane was head and shoulders the best midfielder of the past 30 years at least so he's hardly unworthy to be compared with Messi. Messi's never really done anything for Argentina worth remembering whereas Zidane excelled for some average French sides.