Agreed, hence it is more appropriate to discuss bacterial population in terms of density (that is, number of bacteria per substrate area).

No one is implying that controlled experiments need to be performed by an individual, but it is also overly reductive to say "do it this way" and expect to get the same results everytime.

An absence of appreciation for the biological processes underpinning the biotope you want to establish and a blind faith in any one person's prescription for success are just as negligent as one who doesn't check water chemistry or do water changes.