What will give you more gains?

8 months of both

>>29047
completely dependent on goals. Starting out, focus on compounds. After you "make it" you can start targeting in addition to your compounds.

Mixing both is good

While an isolation-only workout will guarantee exhausting all your targeted muscles, workouts take much longer and you do not improve things like balance or muscle coordination, you only get mass

On the other hand in compounds, usually dominant muscles get to do most of the work and they become exhausted before you can fully exhaust secondary ones, so if you do compounds only, it's possible that you might not be taking full advantage of specific muscles

that's why after compounds you begin isolating your muscles and exhausting them one by one, prioritizing trickier ones (calves, traps, forearms, triceps, etc)