Here's My Two-Cents'-Worth -- the dude with the Epiphone Les Paul 100 avatar
First, you sing how you sing. If he tried not to sing like like himself because he sounds like Hetfield, he might sound like a guy doing a bad Hetfield impression...and it would definitely dam his creative flow.
Besides, if you try too hard to change your vocal style, you can actually injure your vocal cords.
As far as public opinion goes, it all depends. Some bands have done quite well doing their own version of the Led Zeppelin (David Coverdale, Bonham, Katmandu, Fastway, etc.) Black Sabbath (Kyuss, Early Man), AC/DC (Dirty Looks) and many other bands' sound. By that I mean that some of those musicians were mocked for their emulations, and others were lauded. It depends largely upon whether they bring anything new and special to the mix.
For instance, Corrosion of Conformity has a very Sabbath-esque formula to their compositions...but they also have a definite Lynnard Skynnard vibe (and other influences) in there as well, giving them a tasty and identifiable sonic architecture and a fair number of fans.
DA, you mention D. Coverdale, but you leave off Deep Purple, which is where DC got his initial exposure. And yes, they and the bands you mention do not really qualify by present-day standards of "Heavy Metal," but that they are the genesis of the genre is without question, and, I submit, the best and shining examples thereof. But I'll go one step further and add Eric Clapton, Cream, and Jimi Hendrix to the list. Admittedly, Clapton is quite well known for some classic softer songs, almost ballads even, but let's face it -- Slowhand ROCKS! Cream is, of course, just another Clapton format, as was Blind Faith, which while it has the softer edge of Steve Winwood's vocals, nevertheless proudly sports the heavy-rockin' Clapton guitar solos.
Until my personal journey of discovery through Clapton Land, I was convinced that the best, purest examples of true heavy metal were, in this order:
1. Deep Purple [first album released 1968]
2. Black Sabbath [first album released 1970]
3. Whitesnake (particularly the albums 'Ready And Willing' and 'Slide It In') (Although I gladly admit that Steve Vai is a total genius and added immeasurably to the band's overall appeal) [Whitesnake, of course, is a continuation of the Deep Purple effect]
4. Dio [similarly, a continuation of the Black Sabbath effect]
5. Motley Crue [say what you will, their debut album, 1981's "Too Fast For Love," marks the true beginning of modern heavy metal]
6. Metallica [these guys just f****** rock]
7. Iron Maiden [Serious Rockin happenin' here, but they have a small 'egghead probem']
8. [Apologies for leaving others off this list, but that's all that I can think of at this second, although I'm sure there are more.]
I love this thread
Me. too!! Sorry I only found it this late!