What I learned gathering nootropic ratings (2022)

We certainly shouldn't accept subjective evaluations as proof of effectiveness, but that does not give it zero value. The more subtle the effect or the more invested the subject is in establishing the effectiveness of an intervention (or any of many other confounders) the less likely it is to represent proof.

But it is evidence. Think of this as more observational science rather than experimental science; we have to do some work to determine whether it is worth trying to do blinded experiments to validate an effective, and this is that work.