Net calorie an deficit balance

I have two questions:

1. Let's say I must maintain a minimum of 1,500 net calories (calories eaten minus calories burned). If that is the case I must constantly be eating MORE calories than I am burning. That said, what is the point of exercising with the intention of losing weight?

2. My BMR is currently 1,878 calories per day. Assuming I diet WITHOUT exercise and maintain my minimum intake of 1,500 calories, then my deficit is 378 calories.
Now let's assume that I diet AND exercise. Assume that I burn 1,000 calories exercising. In order to maintain my net calories of 1,500 I must consume 2,500 calories. So the hypothetical formula is:

1,878(BMR)+1,000(Exercise)-2,500(consumed)=378(deficit)

This formula implies that I:
A) Have wasted time exercising (with the intention of weight loss)
Will never be able to have a deficit of more than 378 calories without negatively impacting my metabolism.
So my second question is this: How can I increase my calorie deficit without negatively impacting my metabolism.

It's frustrating to know that the AMR(or whatever) recommends creating a deficit of no more than 1,000 calories, yet I can do NOTHING to bring my deficit to this level due to those pesky "net calories."