Interesting so far
What about lagging body parts: say someone only focused on compound movements. Bench press as one for example and was a very shoulder and chest dominant presser with minimal tricep involvement. If they then included tricep isolation exercises are the likely to experience more hypertrophy than someone who has done bench plus tricep isolation for a similar duration?
Using the bench press as an example.
Firstly, it will be very difficult to compare one person to another for many reasons, even using identical twins doing the same exercise, diet and frequency will more often than not produce differant results.
All i can add is, and still use the bench press as the example, within the exercise all muscles (shoulder, tricep, pecs and friends) are moving the weight.
within those muscles the fibre types will differ, just through genetics - and will respond differently, so, the pecs in one person will like very heavy movement for a limeted time under load, while their triceps will perform better with minimal load for a much longer period of time under load.
So logically that person would supplement their training with a movement that isolates (to a degree) the tricep and work that with a lighter load in a higher rep range as well as a heaveir load for a shorter period of time.
but this sort of extra training should not be be done for a long time, no longer than a three month period.