If you add an isolation exercise for the arms to a compound exercise without keeping the total amount of training the same, the extra muscle growth is very small.

Including one isolated arm exercise in a workout routine that already includes compound movements leads to only a small increase in muscle size, even if the total amount of exercise is not kept the same.

Adding more than one isolation exercise for the arm muscles, after doing compound exercises, does not lead to significantly more muscle growth.

Doing more than a basic set of arm exercises and using more than one type of movement does not lead to noticeably greater muscle growth compared to a minimal routine.

When the total amount and intensity of workout effort are kept the same, performing more than one type of isolation exercise for each muscle group does not lead to greater muscle growth.

Doing multiple different exercises with higher volume does not lead to noticeably more muscle growth than doing just one exercise four times per week.