I believe so. To use Poolology as an example, the instructions and math are objective, but I admit that what I see as a 3/8 or a touch thicker or thinner may not be what someone would consider it. So you are correct, imo, that instructions can be objective, but the execution of those instructions could very well be subjective by nature, which throws the whole process into the realm of subjectivity.
I think we need to be careful here. I've said that Poolology seems to be an objective system or method in its raw numbers form as it would then dictate the exact fractional overlap. It would do that for every shot except that you had to change the arcs to straight lines for ease of use. Hence there would be an extremely large number of fractional overlaps.... enough to cover all of the required angles. Again through estimation & rounding of those numbers that large amount of fractional overlaps is reduced to a usable amount for a normal human being & brings in the subjectivity of the analysis portion.
In other methods they start off with a limited amount of visual markers & try to expand on those to cover ALL of the necessary shot angles. THAT involves Subjective Analysis & Application regardless of whether or not the instructions are so called objective instructions.
In others words, even if the instructions could be objective, such does not transform an innately subjective process into an objective process.
Another way to say it is that in any method there are a number of shots(angles) that objectively fit the instructions/visual markers... per the limited visual markers, but no usable 'system' or method is universally objective. Hence the subjective.. whatever one wants to call them... MUST be implemented in order to produce the intended success.
Does that make sense to you... or have I left out some connective tissue out & do you agree?
Best,
RJ