The question is kind of vague to me, it's kind of like asking 'Who is the best guitarist?'
However, you said that you feel people are wrong when they say it is the pinnacle of metal, and I agree. I think they are overrated as the pinnacle of metal, and this is generally true for all the popular metal bands.
But, as Metallica were at the forefront of thrash they had alot of influence extending to other bands.
Kir, I believe that the OP was referring to their general ability rather than an ability relative to their time period. I think lots of bands far exceed Metallica but Metallica maintains a big fanbase, at least compared to these other bands. To me, that seems overrated.