TLDR: I see many CLC fans blaming (G)-idle indirectly for CLC's inability to be "successful" in Korea.
CLC debuted in 2015 and (G)-idle debuted in 2018. There was a 3 year window to make something happen so imo, there's no way (G)-idle should be blamed for why CLC is unable to have a large fanbase in Korea. It's obvious the dynamic of (G)-idle compared to CLC is different. Soyeon writes almost EVERY song for (G)-idle. That's completely unheard of in K-pop. She has written and composed a variety of songs for the group and she knows what the Korean public likes and so (G)-idle developed a distinct reputation despite having a variety of songs. But, I will admit (G)-idle going on Queendom & Soyeon and Miyeon collaborating with League of Legends did wonders for them.
People don't understand that (G)-idle is succeeding more than 4minute ever did, so Cube is taking advantage of that by promoting them more.
CLC simply debuted at a time where G-friend and Twice were dominating, then BP came in shortly. Its tough that Cube Ent. has mismanaged them but keeping it 100, their songs aren't it for Korea's taste and at the end of the day, when you're a K-pop group, being able to develop strong fanbase in Korea is important, more so than an international fanbase.
Cube simply couldn't manage them, so when (G)-idle were debuting and Soyeon basically controls the keys, it relieved a lot of the pressure off of them.
Addressing the quality of music videos, It's simple as this. (G)-idle from debut, have done significantly well for themselves as a group and so the quality of their MVs increased to reflect that, it's simple economics. CLC simply doesn't generate nearly as much revenue as (G)-idle.
So to conclude, it's about timing and unfortunately CLC's direction as a group has not been consistent and when they realized what works for them it's almost a little too late, because (G)-idle overshadows them now.
Thanks for listening to my ted-talk