Veron isn't to blame here. He didn't start the last match and Messi was still spending more time in midfield than in the penalty box. It's a tactical decision by Maradona actually. What it does is that it allows Argentina to penetrate any teams central midfield with Messi's dribbling ability. Sure it means he scores less goals but Argentina are not lacking in the department so it isn't an issue.

Messi isn't required to dribble pass 3-4 people everytime. Just his immediate 1 or 2 markers. The advantage is that if he gets through, the opposition has a serious problem to deal with with a flat backline being exposed.

Maradona actually plays Veron depending on the opposition. Veron didn't start against South Korea but started against both Greece and Nigeria. Veron isn't able to cover as much ground given his age so when more running is needed in midfield Maxi comes in with a change in shape. I think the idea is to use Veron when the opposition sit off and defend deep. Argentina is guaranteed possession in those games and Veron won't be under much pressure to pick out passes from deep.

I think Argentina have been convincing enough. They have no problems scoring goals, have defended reasonably well and the players all seem to be on the same wavelength. Just because Messi isn't scoring doesn't mean that Argentina are playing unconvincingly.