I thought all weekly injections worked the same way

I keep seeing weekly injections discussed for diabetes and weight management, and I realized I was mixing up two very different types of treatment.

I understand that some weekly injections are for weight loss or glucose control, while others are insulin. What I am confused about is whether a weekly insulin injection can replace the insulin routine someone is already using, especially if they take mealtime insulin or premixed insulin.

For people who have looked into switching treatments, how do you compare a weekly weight-loss injection with weekly insulin? What should someone understand before making any change?