My controversial opinion of the day: I think James' singing held back DT from becoming big.
I get the argument, so I'm not saying you're wrong, but I'm still not really sure about that.
They're progressive metal. That alone already makes them a niche band, and by that measure, I think they're already pretty big for their genre. I'm not convinced a different singer with the same music would have resulted in them being huge, even despite the criticism of JLB's voice.
They obviously had the right singer at the right time with PMU, before the music landscape shifted away from that style of vocalist. Even after that, I don't know that anybody who otherwise would have loved their music would have been turned away from Awake by the vocals.
I think it's a more recent criticism, definitely at least post-vocal injury, and their fanbase during the '90s seems totally in line with what I'd expect for a band in their genre in their circumstances, regardless of vocalist.
And during the 2000s, their fanbase has steadily increased to a pretty admirable size. I wouldn't expect any prog metal band to be that much bigger than DT in this day and age.
Could they have done better with another vocalist? It's possible, although I'm just saying that the complaints of JLB's voice alone don't strongly convince me of that.