Yes, of course there are plenty of average to Bad singers in the West as well.
The point is, many of the Mainstream singers/ artists who are very succesful or popular are mostly (exceptions included of course) either above average Singer or rapper or have absolute creative freedom etc.
I wouldnt say thid is the biggest factor why it is hard for kpop Acts to succeed in the West, but i often notice a lot of downlooking upon the skills of the very succesful mainstream kpop artists when it comes to singing, rapping and producing skills.
The point that kpop ifols are not really appreciated as Real srtists, bc their companies control them to an extreme externe, about what they say, how to behave, what to sing, literally everything, make it probably very hard for them to See them as Individual with their very own Repertoire of skills and Talent...