All I can say is that a device shutting off before reaching 0% is usually indicative of a failing battery.
Exactly. Likely when they say top case replacement they did switch out the battery as well. That's because often top case and battery are sold as one part. If you have noted down the battery serial number in the system profiler you can check if it changed and if so, then that means you got a new battery installed.
It would make no sense to replace the top case otherwise as only the keyboard is permanently mated to it. If Apple had only changed the top case, all you'd get is the new housing and a new keyboard. It doesn't make any sense to do that for a battery issue and I am very sure that a new battery was installed with the new top case.
And that should indeed resolve the problem.
Apple will not replace the entire device with a new one if they can avoid it. Apple sets their own warranty terms and they don't guarantee entire device replacements anywhere. This is in the legal fineprint you agreed to when you wired Apple the money. I don't think it's fair to expect a complete device replacement when that was never something you and Apple agreed to before the purchase.
Even by local consumer protection laws you have to give the seller a reasonable option to remedy the issue. For the consumer protection laws in the EU for example this means for smaller issues like reduced battery runtime here a single (!) repair attempt must be allowed. But if it's a major fault then the seller needs to replace the device. For example if a brand new Mac dies completely, that's more of a major fault than some charge issue as the device is now completely unusable. Waiting weeks for a repair is out of the question then. Even then you have to specifically request a replacement under that law, by default Apple will attempt to treat it as a regular warranty case and will repair it. They will never voluntarily offer it.
