I'm oversimplifying and doing some guesswork here, but this is my take: His natural and most comfortable range is high baritone. He can hit some VERY high notes, but cannot sustain singing in that higher register for extended periods. In his younger days, he could get away with it by pushing and straining, and singing in falsetto. But as he has aged, that ability has left him due to just age, wear and tear from improper singing technique, and wear and tear from living a...er..."rock and roll lifestyle" (if you know what I mean). So, he has lost some range and stamina, for probably a variety of reasons.
To me, this has been evidence for a long time. I know Samsara disagrees with me on this, but I will hold up his time in Journey as an example. He was with them in 2006-2007. And while I liked him a lot as a vocalist, I absolutely felt that he was the wrong choice for the band back then, at least in terms of being able to perform the old material (I would have been completely open to hearing a new album with him where they could write stuff that more suited his style and range). I saw them live on that tour when they co-headlined with Def Leppard. He sounded great on some songs. And his stage presence was awesome. But he cheated on a LOT of notes. And even with Deen taking lead vocals on some songs to give him a break, his voice was noticeably losing power and range as the show wore on, and it was clear to me that, although he could fake it for a few songs, that Steve Perry range wasn't comfortable enough for him to make it through an entire set.
I'm late getting back to this. Sorry. Busy weekend, busy day at the office. Wait, we don't fundamentally disagree on JSS singing classic Steve Perry Journey full time. No, he's a high baritone these days. His range has dropped, and while he could, and did cheat to sing some of those Perry songs in normal tuning, and it was cool to hear, the real HARD stuff was sung by Deen Castronovo (from behind the kit). My point on JSS and Journey, was that they could have embarked on something DIFFERENT by honoring their agreement to bring JSS on full time, and having him and Deen split lead vocals. JSS would get probably 65 percent, with Deen getting 35 percent, and the more difficult ones. Leaving JSS to do stuff from Trial By Fire, the classic stuff he felt good about, and maybe even the pre-Perry records.
My only point when we saw that show (and I disagree that JSS lost power. I have the recording somewhere, and if I wasn't so lazy, I'd prove you wrong), was that Journey sounded really, really good with the two of them (JSS and Deen) singing. It was different, it was a cool vibe, and I would have loved to have heard it from that point forward. That's why I was so stoked when Journey did agree to move forward with JSS, and then so upset when they reneged and kicked him to the curb for Arnel (who I also obviously like). I just wanted them to continue with something different, and instead, they got someone whose voice was closer to Perry's to sing most of the material (Deen also took on a couple songs to help Arnel as well during Deen's tenure in the band).
The funny thing about Journey is, before Deen went off the deep end and was kicked out of the band, he was the singer they've always wanted. HIS voice is the closest to Steve Perry they've ever had. He was just too shy to be a frontman and stand out there in front of everyone. I was lucky enough to catch Deen Castronovo fronting Neal Schon's JOurney Through Time earlier this year. Deen was sick with a bad cold, and still sounded like this:
https://www.youtube.com/watch?v=mgqbLDb5gbY And I made a promise, after Journey screwed over JSS, that I'd never go see Journey again, even though I love Eclipse, the last record with Arnel. Just out of a sense of respect to JSS. And I've held true to that.
But clearly, JSS is a baritone, and as you rightly pointed out, it appears his comfort area these days is as a high baritone.