pH impacts growth for sure.. you'll need slightly different ratios of nutes are varying pH, because it can affect availability, meaning a new balance is required. You can find real research that shows optimal pH (per species) can definitely impact growth rate. Even if such things are measurable, relative to common sense ranges, it's a small thing. e.g. there's no way the uman eye can see a difference between 5.8 and 6.0 - not with all the variance you get seed to seed as well as a number of other volatile factors muddying the waters.
with that said, i rarely pH test my water. I have a 100-pack of ph strips that are 2-3 years old at this point and there are at least 80 in there. Been over a year since i ph-tested anything i bet. My nutes are ph-buffered, though, so it's ~6.0 everytime. Takes the guessing game out of it. So, there are ways to avoid the problem with confidence. I have terrible habits with my reservoir, too, and still no problems. If i were smart, i'd test it before germinating seeds.. but i'm lazy.
Consistency is probably most important, relative to any common sense range of pH.
Genetics is your potential. You either let the plant get there or hinder it. There's no polishing turds, here.
