What research? Multiple companies which use these practices have grown from zero to trillion+ dollars in market cap, so I find it hard to believe the narrative that all of it is useless and ineffective.
It doesn't have to work. Your customers just have to believe it works. Even just have to believe it might work, since they are looking for any competitive advantage. You need research to show it help just as much as you need research to show it doesn't.
I think you will find both sorts of research, because it seems obvious that results will depend on what sort of web site you run and what sort of audience you have.
