Your logic looks fine. The point isn’t to get some thing for free, but to avoid the negative feelings. Sometimes money can solve the problem… Sometimes it won’t, and a return is better. The point being, if you’re legitimately unhappy, then negotiating for cash or value are a common technique to address the situation. They might be willing to do cash back, or they might simply say if you don’t like it then return it.
There is a prior example here (different company), that corrected a problem and satisfied their customer with a partial refund.
https://forum.mattressunderground.com/t/memory-foam-mattress-weight