If you're not satisfied with the computer, and you can return it for a full refund - that seems like a good choice while you figure out what you want to do instead. This is no indication in itself however, that there's anything wrong with the computer hardware.
Besides that your question and the accompanying forum threads seems to be incoherent:
1) You experience high CPU load when using Lightroom. This is shown with screenshots of Activity Monitor showing high CPU load for Lightroom.
This is due to the programming of Lightroom. It is not a hardware error (!).
The posters on the forum saying that this is a cooling error are wrong. If the system was sensing a cooling problem and artifically making the CPU load higher due to this, it would have been attributed to kernel_task and not Lightroom.
2) You write that you were using the same setup in '93. This doesn't ring true as services such as Slack and Spotify did not exist in 93, nor was tabbed browsing a thing... heck you would have been using Mosaic or similar at that time.
3) As far as I know, chain stores get the exact same products as any other Apple vendor. There's no such thing as low-quality Apple batches being sold at chain stores at discount - at least nothing official. It might be that specific demo units or defective units can be sold as one-offs by a chain store, but they would have to advertise it as such. Advertising them as the real thing would be false advertising.
4) It is unclear, but it seems your problem is that your hear fan noise when you think you're not really doing anything with the computer. Try starting the computer up in Recovery mode (hold down Cmd and R while booting the Mac). If you hear excessive fan noise here while the computer is running known good software and not doing anything, that would be an indication of hardware failure.
