If you spent £1200 on an apple, bit down and it tasted of lemon, wouldn't you feel inclined to choose another grocer? 😉
No, not at all. Nothing is perfect, you expected too much. I'd return the fruit. If they hassled me for awhile and gave me nothing, then I'd never return. If every fruit I'd tasted had been bad, but their other offerings were better, I'd still buy there, but would avoid their fruit. If every other place I went to was just as bad, I'd find alternatives, or even accept the least reprehensible. If they offered me another piece of fruit, even if it wasn't perfect, if I felt it was apt, I'd accept it. If they offered a partial refund and a replacement, and the replacement was good, I would want to shop their in the future.
For the record, I'm not saying Apple is perfect at all. Some will be bad, it happens. I would have taken the replacement. My MBP works great, as does my MP. I've had issues with them, as well as other Macs, but I've had far worse luck with PCs. I also work with Macs, and in the hundreds I've deployed, only a few have had issues.
You expected far more than reality dictated, were disappointed with the results, were offered a partial refund and a replacement, but expected the worst and sent it back. That's fine I guess, but it doesn't make sense to me. Especially since you're just going to get another later, possibly even a lesser, but cheaper model. I think
bv put it best though. Here's hoping you come back when you get the new one and you're not as hyped about it so you won't be so disappointed.