Nelson is a good fighter, decent at best, but is not close to the top 5 - 6 IMO. He has strengths which are evident to see, hell the man did it all without a camp which is freakish, but hes maxed out his potential and can not climb any further than he already has. The HW division is too good for him now, hell there was a time when Brandon Lee Hinkle was considered by some to be near top 5
It all depends on who is fighting around you, stylistically hes awkward and has a great chin but Cain, JDS, Overeem, Lesnar (yes, i said Lesnar!), Bigfoot, Werdum, Kharitonov, Carwin - the name guys right now would all beat him one way or the other. Running guys close in fights you lose does nothing for you if you keep losing, sorry to say.