I do think the idea behind snap isn’t all about pushing the Linux platform as such forward, but to specifically gain a market advantage to Ubuntu.

Why else is finding documentation for changing the default store so difficult? And I don’t think you can even have multiple “repositories” there–quite unlike all other Linux packaging systems out there. (Corrections welcome!)

Another way to check is to

strace cp testfile testfile2

and the sequence in which the message is printed and operations performed can be studied.

It’s perhaps a lot to read, but linux tracing tools are worth learning!