The source for this is from a bunch of places, so I’ll point to the Search Engine Land post that links to many of them.
The points describe that Google AdWords landing pages that load slower can have a negative impact in your positioning. It does make sense that this would be included in Google’s Quality Score.
There are other reasons to create unique landing pages, but this could be a great client-communication opportunity for search marketers to suggest targeted, yet fast-loading landing pages.
It’s no secret that clients would just rather you point the ads to the most relevant pages on their site. It makes it easier on them. It’s also no secret that many of these pages may take longer to load.
If the client or business is smaller, it might be an easier sell. The communication lines are smaller and it won’t take as many hours for them to create these landing pages.
If the client is larger and your contact is a marketing director or something similar, it can be more difficult. They love your idea, but they also have their own processes. Their lines of communications are larger, and the number of hours it will take for them to develop these landing pages can be enormous.
This isn’t a good or bad thing. It’s just “what it is” and should be understood within communication.