do dance and singing tiers actually exist?

The rank tier you talk about doesn't exist in the industry. It's more a trend that stems from tiers lists that are used to classify everything and anything.

However, there is a form of classification for singers, rappers and dancers in kpop that exists within groups. Main > Lead > Sub > No title

skill level is not subjective so idk what exactly you’re asking… yes things like support can be judged as better or worse…are you perhaps asking if the way the tier list is structured is something universal? I don’t believe so. It’s something that started when people realized making vocals analysis videos on YouTube gave people clout lol. I still remember how many videos existed to prove Taylor swift can’t sing or is a poor vocalist lol.

My faves are SSSS+++ tier

Yes

In Dance there is Lee Taemin tier and everything else below it