It's the same thing with vitamin c intake to keep a person from getting scurvy... that's why we have an RDA amount. Or propofol amounts to keep a person sedated... that's why we have standardized doses based on body weight, etc. The human body is very similar from person to person. The amount of test needed to sustain gains will vary a little based on your weight, and gender, age and sometimes lifestyle but not drastically especially not based on genetics.
I'll go as far as to say there probably isn't a healthy young sub-200 lb man alive who naturally has a test level of 400 and cannot sustain their gains naturally without cruising/"trt." And even if he stops working out or gets sick and loses weight for some reason, he'll have muscle memory to regain it quickly.
Cruising is simply not needed in that scenario. And you won't find a doctor or credentialed medical expert who disagrees with that, even at some of the more shadier clinics.
