Ok, lets say all this can be true. I believe some idols already had enough time to become better singers, if they were good singers they should bea able to sing well by now. How can we considered this idols amazing or just good singers if they cant reach the note and their voices crack many times? they dont sound nothing like the record version. I mean, nobody considers Lia a great vocalist, i and many more believe she have a nice tone, but she needs alot of work, she is not a good singer. Meanwhile, for example, many fans believe Jimin or Tae are good vocalists. And i cant tell you this, Lia, Jimin and Tae have good "Live performances", but in encores suffer alot to sing their own songs. How a good singer cant reach the note of their own song? also, i cant think of any good singer that cant sing well without the in-ear thing, only can think in bad ones.
Honestly don't think you pay attention to singers enough to know who does and doesn't use in-ear. THEY ALL DO because in big venues where the crowd or music is loud or when room acoustics are messed up they need to be able to hear themselves sing. There are countless videos of singers like Beyonce and Ariana Grande taking them out and putting them back in constantly throughout concerts for this exact reason. Adele famously had issues with hers at the grammys when singing all I ask and was totally off pitch. I honestly don't know any famous singer who doesn't use them.
Note I'm not in any way saying these idols are amazing or even good, just that your thinking is a little linear. Repetition doesn't mean a direct increase in quality. For example, if you take hundreds of photo's a day, sure your quality will increase slowly over time, but not as fast as if you had a teacher giving you feedback and if you stop lessons half way, your not going to be as good as someone who is consistently taking lessons and getting feedback. meanwhile there are some who excel with little to no guidance would be considered geniuses, and those who rarely take photo's are going to see far less improvement no matter the amount of time. IMO its the same with idols, for alot of idols the most time they spend singing live is in the studio where they aren't going to get feedback because the have someone ready to 'fix' their voice. Separate from this I do agree that if your making me pay to hear you sing it needs to be live and with some quality so I expect a level of professionalism by you getting lessons. But I do appreciate that for most, their schedules are so packed they literally have no time and the companies aren't going to make finding time for lessons a priority.
Many idols get taught bad or incorrect techniques that over time damage their voices because the companies want a specific sound and lots of work is done in post production to fix it (why else is SM convinced they can make literally anyone an idol?). We have long known that many of the 'live' videos are anything but to cover all these issues and whilst they aren't the best singers, bad choices in song, lack of training and technique make it far worse. Take momo for example, predebut she used to skip vocal lessons because they were so difficult for her (the JYP half air method be damned), for years we've known her natural voice is far lower than what she puts out in Twice and misamo confirmed it on every track, yet she consistently is made to sing far higher than she can handle. Is she a great singer? no, but how can she get better/sound better when the songs aren't even in her range to practice with a teacher and shes fighting to be on pitch even in the recording studio? IMO there are plenty of idols on par with her or even worse, BUT being made to sing outside her range made it far more visible whilst other companies are far better at hiding it and choosing songs that suit their groups ranges.
