Muscle is built out of protein, but eating protein doesn't build it on its own. Training places the order. Protein delivers the bricks. Sleep is when most of the building gets done.
Protein is a long chain. Your body can't use it whole, so it gets cut up, shipped, and put back together where it's needed.
You need both. A hard lift with no protein is an order with no bricks. Protein with no lifting is bricks nobody asked for.
Same Ian, same day, same training. A proper serving of protein switches building on for a few hours. Each meal is another chance to flip the switch.
You don't get stronger in the gym. You get stronger in the hours after, and most of that repair happens while you're asleep.
Short answers.
Pick one.