Totally agree he's not underrated, but someone can be ranked really highly and still be underrated. In his case though, yeah, he's ranked between 5-7 in most lists, something like that....you can argue he could be higher, you could argue he could be lower, it's not that obvious, so certainly not where I'd suggest there is something wrong here, guy is seriously underrated....
Whenever someone talks about overrated and underrated, I always start with how they are rated first, for obvious reasons, but a lot of times people forget that. As an example, everyone on the planet may agree that player X is the best player in the world, including me, but I could still suggest that player is overrated depending on how he is rated. That rating would obviously need to go beyond simply being rated #1 of course....it would go along the lines of suggesting the player is the best, 3 tiers above the next best player, close to Gretzky's level, etc......if that is a general sentiment for someone, I could very well suggest they are the best but overrated at the same time.