Let's examine that for a moment.
Live, the lead singer sings to a backing track because the other guys in the band are all wearing masks that would make singing impossible. One one hand its understandable, but on the other it is cheating a little.
There are dozens of variants in, lets say Overdrive, you can put into your delivery of vocals before reaching full on saturation. My objection isn't that Tobias Forge (the guy that has been outed as the singer for Ghost) sings clean, its that his vocals are flat, slightly nasal, and lacking in dynamics. There are dozens of metal singers from the 70s and 80s that sang "clean" but still had inflection. Tobais doesn't need to yell or growl, but emoting just a little would be nice.
Part of me wants to like these guys, but the vocals are a deal breaker for a lot of people. There is passion in the music that calls for vocals that are far more soaring than what is being offered. Someone pointed out to me once that they thought he sounded like the vocalist from They Might Be Giants. TMBG are a funny band, but no one has ever said John Linnell has an epic voice.
The singers of other retro-rock bands like Witchcraft, Graveyard, and The Vintage Caravan all sing clean but manage to get a little fire in their voices when they need to. If Ghost could manage something like that, I'd be down for them.