Yes, it's confusing.

> I pay a $10 co-pay for generic with my insurance, but when I pick up from pharmacy the receipt says "you insurance saved you $1888" (you're right it's not ~$2500/month - I just checked and that's a different prescription I have that I get filled at the same time).

As a rule, the "your insurance saved you $X" is a meaningless statement.

It's actually worse than meaningless - it's effectively an advertisement for health insurance, not an actual statement of fact. It's calculated based on the difference between what you paid and the list price for a drug, which almost nobody is paying (and your insurer is definitely not paying).

Your insurance pays some other negotiated rate for drugs - they will basically never pay list price. Even if you were getting it without insurance, you still would likely not be paying list price. If you were paying out of pocket, you'd probably be using a discount coupon (which usually works as a third party functioning as a pseudo-PBM, a ridiculous concept which I will not bother to try to explain in this post). Or your doctor would explicitly prescribe the branded version ("dispense as written") and you'd be using the Gilead copay assistance coupon to pay for it.

Since there's no situation in which the list price is what you'd be paying, it's completely meaningless to say "you saved $X off the list price". I'm half of the mind that these statements should be banned by the FTC as a deceptive trade practice - that's how misleading they are.