Do you belong more to souce first or to speakers first school of thought ?

Garbage in is Garbage out 

We are not interested in garbage, we are talking about excellent or better source and similar level speakers.

In many systems, the source is at least physically easier to replace than the speakers. What does that count for, if anything?

Clearly any speaker will have the greatest impact on overall sound quality and it’s also the source of greatest distortion. All other components deliver significantly less distortion.  To get the best out of a high end speaker will require better electronics especially source components. The correct balance is impossible to determine precisely. Ultimately it’s a function of what you can afford and trial and error is your only guide.

Recordings also often have a lot of distortion.