In terms of deciding who's "new", I'm going to treat for the sake of this post that you are referring to K-pop performers who have debuted within the past two years, and so I might try to answer your question from that angle.
In determining who qualifies as an "all-rounder", I think it would be a reasonable assumption to say that some idols could be considered as "all-rounders" if they had a longer training period compared to those who don't, because they would have had more opportunities to practise and hone in on their craft, while juggling between school work, attending (music) academies and engaging in other extracurricular pursuits.
I also like to take into account other things about the performers themselves — namely, I would like to know, for instance, about the length of the idol's training period, and what they did during their training period, because some idols may have some long training periods, but they might not necessarily been set on the path originally for that. That is, some idols may have received training to become actors, but decided to switch paths, say from acting to performing, to improve their overall prospects. But, of course, there are idols who may continue to practise even after having received training, because training only often fulfills the "basic requirements" of what is expected from the job, and even though they may not debut originally, or be recognised, as all-rounders, they could be eventually regarded as such.
The other thing I sometimes like to know is where the idol studied because the idols of today would be considered more well-off financially than those who debuted from previous generations and with some attending art schools, which would be seen as a privilege because it is not considered as a standard education in South Korea. Also, sometimes these idols may also be receiving training at academies, which is sometimes where they are recruited by agencies. Also, being here (at the academy or at their company) gives them access to opportunities, such as mentors and the like.
Sometimes, the centers chosen to represent the group during their performances can also indicate which members would be considered as "aces" or "all-rounders". And sometimes before debut, agencies, in promoting their groups, endorse particular members by describing them as having "outstanding performance ability", which makes identifying these specific type of people easier.
If you want some names of male idols, though: Won Bin (Riize) Zhang Hao (ZB1), Sung Hanbin (ZB1), Seok Matthew (ZB1), Dohoon (TWS), Jaehyun (BND); and for female idols: Rami (BM), Asa (BM), Ahyeon (BM), Natty (KIOF), Julie (KIOF). And there's more names that I haven't mentioned either, but those are the few names that came to my mind.
the abilities of a performer are still a big factor for me. But it seems most people these days just want a celebrity, whether they are any good on stage is an after thought. And the bigger companies in particular know this.
