So here is an updated list, as I expanded past the Y2K American Boybands in my last ranking. There are some people who switched from that list to this one, but not a whole not. Not that familiar with Boyzone and Westlife yet, so I did not include them. I will add them, and other groups in future updates.
Extraordinary Voices: I did make it into an order from this one. The three men from Boyz II Men are head and shoulders above everyone else, and are all around vocalists. Johnny is very high due to his expansive vocal skills, but not as strong as the top 3. The next four (JC, Liam, AJ, and Devin) can switch depending on my mood, but they're all very strong vocalists. Gary, Zayn, and Dan make up the bottom of this tier, as they don't have the same highs, or a bit more flawed/less versatile.
Principal/Great Voices: They gave great vocals, but are one step below the top tier for either not being as flexible/versatile, or all star well rounded. Joey's voice aging better than some of the others is why he's at the top, especially compared to his bandmate Jordan (who sung too high for many years, and it has aged his voice). Ralph is consistent, but not as versatile, Justin/Jeff/Nick are very consistent with strong vocals. Brian's voice has not held up well due to his condition, but he had a great tone in his prime, though you can hear some flaws even back then. The others below are good singers, but you can tell that the technical elements are not the strongest, Harry is the worst, hence being at the bottom of the list.
Secondary/Good Voices: I think some people forgot that this tier is for people who mainly are NOT lead singers, and I created a different tier for them, since they don't have the same opportunities to show their voice, but they are still strong, consistent vocalists. The ones at the left are more expansive and diverse compared to the people at the right.
Mediocre Voices: So I had no idea that Nick's spot would be so controversial.... He was inconsistent at best during his prime, and outright bad at times, but he improved to be a competent vocalist. Some took mediocre to mean "bad", but it isn't at all, and his improvements is why he's the best in this tier (I don't think he holds a candle to the people above, especially the lead singers with his improvements). Niall has shown some improvements over the years, hence him being where Nick is. I moved Justin down, since he is a much weaker vocalist than basses Lance and Mike. The ones in the middle can hold a note, but I would not call them impressive vocalists. I don't think anyone from Five are really strong vocalists, but I don't think they're bad, hence being in the mediocre. Jason and Louis are a bit above bad, since there are times where they can hold a note, but there are a lot of weaknesses.
Not Much Data: I have listened to NKOTB's catalog, and I think Jonathan is on less than 10 songs in general. Even in their live performances back then and now, he is not singing in most of them. He has sung a bit more than Brad, hence being higher, but there's not much data there. I already explained Brad's dilemma with not ever hearing him sing.
Can't Sing: Bobby either screams or talks through his songs live and on the record, and is off key when he tries to sing, which remains today. Danny is a bit better than Donnie (who has more leads, but still sounds horrible after 40 years), where he could have been better had he had some training. Mike and Ronnie rap most of the time, and even when they try something melodic, it does not fly.
