The creation / terminology just ranks them based on power, which is something Oda has done since East Blue. He's not changed it yet, so there's no reason to treat these guys any different than Kuro's crew with powerscaling.
Okay, then define a YC1, YC2, YC3
There is no System for that...
Take Benn, Yassop and Lucky as example, they all got ''hyped'' and got mentioned by sengoku as People who made a Name for themselfs even tho while being under a Yonkou. Were BM's commanders mentioned? No. Were Kaidou's commanders mentioned? No. Because Shanks commanders got more ''hype'' they have to be somewhat above them - i guess? So how do you rank them? YC1++, YC1+, YC1?
Oda didn't gave us any ''system'' to that - it was made up by the fanbase...Katakuri, Smoothie and Cracker are commanders. That's it. No YC1, YC2 and YC3. Katakuri is the strongest of These 3, stil a commander. Smoothie is YC2? Based on what? We haven't seen anything from her. Based on her Bounty? But you guys say bounty's doesn't mean anything.
Look at Kaidou's commanders.
King is YC1, Queen is YC2 and Jack is YC3. Based on what? Because it ''HAS TO BE LIKE THIS''? Who says that?
What makes King YC1 and Queen YC2? Non of them showed superiority over the other nor did we got any Information of who is above who. Then People start saying ''So you think Kaidou has 2 YC1???''...
See? This whole System Limits the view of People. Katakuri might be the strongest commander even when counting in Kaidou's commanders - who knows? But it doesn't mean Katakuri can beat any commander with Zero or low difficulty, that's just not gonna happen - it will be a Long and hard fought fight ''even against YC3''. And Katakuri is kinda Special because of his overpowered CoO.
Like i said, 1 commander can beat another commander - same as one Admiral can beat another Admiral or Yonkou beat another yonkou, but it's ''unproductive'' to make different ''levels'' out of that.