I think the comp title is also just a quick and concise way to give the reader, upon first glance, what the book is about/what concept to expect etc. without having to use so many words. It's like the elevator pitch. Trying to pitch someone a mouth full could just confuse or lose them. X meets Y gives a clear picture right away: this is why you want this book, this is what you can expect, etc.
A book selling on its own merits ... I mean, the only way a book would sell on its own merits is if you read that book first and then decide if you want to buy it. Every book is pitched in some way and relies upon marketing blurbs, pitches, etc. And there's always a chance you can read the marketing blurb, which will ALWAYS be written in a way to make the book as appealing as possible, and then be disappointed at the actual book because the contents of the book didn't match up to marketing blurb. The whole point of marketing is to make as many people as possible read the book.
The only thing I don't like about the comp title is when certain properties are overused. The whole Game of Thrones comp title nonsense is just a lazy way of saying it's fantasy that includes court intrigue, which, what fantasy doesn't, but this is the short hand publishers are currently using/overusing and readers will get tired of it. Tbh, GOT is starting to get used by pubs just to denote fantasy in general and these books are starting to blend together. If every fantasy is Game of Thrones meets X then regardless of what that X is, none of these books will really stand out from each other.